Astronomy Picture of the Day Search Results for "Mars"

APOD: 2009 January 19 - Methane Discovered in the Atmosphere of Mars
Explanation: Why is there methane on Mars? No one is sure. An important confirmation that methane exists in the atmosphere of Mars occurred last week, bolstering previous controversial claims made as early as 2003. The confirmation was made spectroscopically using large ground-based telescopes by finding precise colors absorbed on Mars that match those absorbed by methane on Earth. Given that methane is destroyed in the open martian air in a matter of years, the present existence of the fragile gas indicates that it is currently being released, somehow, from the surface of Mars. One prospect is that microbes living underground are creating it, or created it in the past. If true, this opens the exciting possibility that life might be present under the surface of Mars even today. Given the present data, however, it is also possible that a purely geologic process, potentially involving volcanism or rust and not involving any life forms, is the methane creator. Pictured above is an image of Mars superposed with a map of the recent methane detection.

APOD: 2008 November 24 - Radar Indicates Buried Glaciers on Mars
Explanation: What created this unusual terrain on Mars? The floors of several mid-latitude craters in Hellas Basin on Mars appear unusually grooved, flat, and shallow. New radar images from the Mars Reconnaissance Orbiter bolster an exciting hypothesis: huge glaciers of buried ice. Evidence indicates that such glaciers cover an area larger than a city and extend as much as a kilometer deep. The ice would have been kept from evaporating into the thin Martian air by a covering of dirt. If true, this would indicate the largest volume of water ice outside of the Martian poles, much larger than the frozen puddles recently discovered by the Phoenix lander. Such lake-sized ice blocks located so close to the Martian equator might make a good drinking reservoir for future astronauts exploring Mars. How the glaciers originally formed remains a mystery. In the meantime, before packing up to explore Mars, please take a moment to suggest a name for NASA's next Martian rover.

APOD: 2008 October 6 - Layers of Cliffs in Northern Mars
Explanation: How did these layers of red cliffs form on Mars? No one is sure. The northern ice cap on Mars is nearly divided into two by a huge division named Chasma Boreale. No similar formation occurs on Earth. Pictured above, several dusty layers leading into this deep chasm are visible. Cliff faces, mostly facing left but still partly visible from above, appear dramatically red. The light areas are likely water ice. The above image spans about one kilometer near the north of Mars, and the elevation drop from right to left is over a kilometer. One hypothesis relates the formation of Chasma Boreale to underlying volcanic activity.

APOD: 2008 August 12 - A Mars Panorama from the Phoenix Lander
Explanation: If you could stand on Mars, what would you see? The robotic Phoenix spacecraft that just landed on Mars in May recorded the above spectacular panorama. The above image is actually a digital combination of over 100 camera pointings and surveys fully 360 degrees around the busy robotic laboratory. Clicking on the horizontally compressed image above will bring up the extra-wide uncompressed version. Visible in the image foreground are circular solar panels, various Phoenix instruments, rust colored rocks, a trench dug by Phoenix to probe Mars' chemical composition, a vast plateau of dirt and dirt-covered ice, and, far in the distance, the dust colored atmosphere of Mars. Phoenix landed in the far north of Mars and has been using its sophisticated laboratory to search for signs that past life might have been possible. Recent soil analyses have confirmed the presence of ice, but gave conflicting indications of unexpected perchlorate salts. Whether perchlorates exist on Mars is now being aggressively researched, as well as what effects perchlorates might have had on the past development of life.

APOD: 2008 July 23 - High Cliffs Surrounding Echus Chasma on Mars
Explanation: What created this great cliff on Mars? Did giant waterfalls once plummet through its grooves? With a four-kilometer drop, this high cliff surrounding Echus Chasma, near an impressive impact crater, was carved by either water or lava. A leading hypothesis is that Echus Chasma, at 100-kilometers long and 10-kilometers wide, was once one of the largest water sources on Mars. If true, water once held in Echus Chasma likely ran over the Martian surface to carve the impressive Kasei Valles, which extends over 3,000 kilometers to the north. Even if initially carved by water, lava appears to have later flowed in the valley, leaving an extraordinarily smooth floor. Echus Chasma lies north of tremendous Valles Marineris, the largest canyon in the Solar System. The above image was taken by the robotic Mars Express spacecraft currently orbiting Mars.

APOD: 2008 July 14 - Changes in Angular Mars
Explanation: Does Mars always appear the same? No. As both Earth and Mars orbit the Sun, the apparent angular size of Mars changes as viewed from the Earth. Pictured above from Enschede, Holland, Mars was captured in 2007 and 2008 with 30 separate images, all taken with the same magnification. When Earth and Mars are on opposite sides of the Sun, Mars appears relatively small. Conversely, when Earth and Mars are near each other, Mars looms large and bright. The largest Mars has appeared in recent history was the opposition of August 2003. Since Mars is always more distant from the Sun than the Earth, Mars never shows a crescent phase to Earthlings. Visible also in the above images are the north polar cap of Mars, dark and light soil, clouds, and, in the early images, a global dust storm. The next opposition, when Earth again passes near to Mars, will occur in early 2010.

APOD: 2008 June 8 - Mars Soil Sample Ready to Analyze
Explanation: What surprises are hidden in the soils of Mars? To help find out, the Phoenix Lander Phoenix Lander which arrived on Mars two weeks ago has attempted to place a scoop of soil in Phoenix's Thermal and Evolved-Gas Analyzer (TEGA). Pictured above, the dirt-filled scoop approaches one of TEGA's eight ovens. Once in the oven, a soil material will be baked and the emitted gasses categorized by a mass spectrometer. Quite possibly, some of the light colored material visible in the scoop has the same composition as the light material imaged near the foot of the Lander, which may be ice. Phoenix is scheduled to spend the next three months digging, baking and chemically analyzing its immediate surroundings to better understand Mars and whether the boundary between ice and soil was ever capable of supporting life.

APOD: 2008 May 25 - Phoenix Lander Arrives at Mars
Explanation: Will Phoenix survive its landing today on Mars? Phoenix's landing sequence will ramp up starting at about 7:30 pm EDT (23:30 UTC) today and last just over an hour. If all goes well, one of Phoenix's first images from Mars will appear on APOD tomorrow. The Phoenix Lander is programmed to set down near the North Pole of Mars, and, over the next three months, sample alien soil and ice and look for conditions conducive for ancient microbial life. Shown above is an artistic animation of what it might look like to see Phoenix land on Mars. In the animated sequence, the Phoenix spacecraft arrives at Mars, deploys its braking parachute, jettisons its heat shield, fires it thrusters, lands, unfurls its solar panels, deploys its instruments, scoops up some of Mars, and begins its analysis.

APOD: 2008 May 19 - Flying Over the Columbia Hills of Mars
Explanation: What it would be like to fly over Mars? Combining terrain data from the orbiting Mars Reconnaissance Orbiter spacecraft with information about the robotic Spirit rover currently rolling across Mars has resulted in a digital movie that shows what a flight over the Columbia Hills might look like. Dark rippled sand dunes are highlighted against the Columbia Hills in the above opening image. Clicking on the above image, though, will launch you across Mars, approaching the Columbia Hills. On the far side of the hills, the dark sand dunes come into view. Soon you pass an unusual white-rimmed structure, slightly raised, known as Home Plate, the origin of which is currently unknown and being researched. Turning, you re-approach the hills from a different angle, this time zooming in on Spirit, a curious alien rover sent from planet Earth. A final zoom pans out over the region. This coming Sunday, NASA's Phoenix Lander will attempt to set down near the icy North Pole of Mars and search for signs of ancient life.

APOD: 2008 May 11 - Retrograde Mars
Explanation: Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars in Earth's sky is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars as they orbit around the Sun. During the most recent such pass over the last year, the proximity of Mars made the red planet appear larger and brighter than usual. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion. Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop in the sky. Near the top of the loop, Earth passed Mars and the retrograde motion was the highest. Retrograde motion can also be seen for other Solar System planets.

APOD: 2008 May 10 - Stars and Mars
Explanation: Wandering through the evening sky, on May 4th planet Mars stood in line with Castor and Pollux, the two bright stars of the constellation Gemini. In this time exposure of the celestial alignment, Mars actually takes on a distinct yellowish hue, contrasting in color with Pollux; a giant star known to have a Jupiter-class planet, and Castor; itself a multiple star system. Though in mythology Pollux and Castor are twin brothers, the two stars are physically unrelated and are about 34 and 50 light-years distant respectively. Included in the skyview are Procyon, alpha star of Canis Minor, and famous star cluster M44 also known as the Beehive Cluster. Dust in our own solar system reflecting sunlight creates the faint band of Zodiacal light emerging from the lower right corner of the frame. Just put your cursor over the picture for help with identifications. Of course, bright Mars can still be found in the western evening skies and tonight wanders near the crescent Moon.

APOD: 2008 April 14 - Phobos: Doomed Moon of Mars
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so Phobos will likely be shattered by stress caused by the relentless tidal forces, the debris forming a decaying ring around Mars.

APOD: 2008 April 7 - Mysterious White Rock Fingers on Mars
Explanation: What caused this unusual white rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate that this is not correct. The light material appears to have eroded away from the surrounding area, indicating a very low-density composition, possibly consistent with volcanic ash or windblown dust. The stark contrast between the rocks and the surrounding sand is compounded by the sand's unusual darkness. This picture was taken from the Mars Express spacecraft currently orbiting Mars. Planetary scientist Emily Lakdawalla, among others, has followed her curiosity about this unusual Martian landform into a fascinating investigation that is eloquently described in the Planetary Society Weblog. The mysterious white rock spans about 15 kilometers across inside a larger crater that spans about 100 kilometers.

APOD: 2008 March 11 - An Avalanche on Mars
Explanation: What caused this sudden cloud of dust on Mars? An avalanche! The first avalanche imaged in progress on another planet was recorded last month on Mars by NASA's robotic Mars Reconnaissance Orbiter. Visible in the above picture, digitally rescaled, are several layers of white ice thawing over red rock, with darker colors toward the right indicated Martian soil that mixed with lesser amounts of ice. As the cliff of over 700 meters high was thawing, falling ice crashed down raising plumes of ice and dust so thick they cast visible shadows. The scarp has slopes with grades greater than 60 degrees. The entire scene is illuminated from the upper right by the Sun. A thaw occurs each spring in the Northern Hemisphere of Mars, as the warming climate causes solid carbon dioxide ice to sublimate directly to vapor. Studying such avalanches allows planetary geologists to better understand soil configurations on Mars.

APOD: 2007 December 23 - Moon and Mars Tonight
Explanation: The Full Moon and a brilliant, ruddy Mars will share the sky tonight. Skygazers can easily enjoy the celestial pairing as the two are separated by a degree or even less. In fact, seen from parts of northern North America and Europe, the Moon will actually occult (pass in front of) the Red Planet. Mars is so bright because it is near opposition, opposite the Sun in Earth's sky and near its closest approach to planet Earth. But Mars is not nearly as bright as the Moon, also opposite the Sun tonight. In this striking preview of tonight's sky show, backyard astronomer John Harms was able to photograph an almost Full Moon near Mars last month. His simple, single exposure relied on clouds to block some of the overwhelming moonlight.

APOD: 2007 December 18 - Unusual Silica Rich Soil Discovered on Mars
Explanation: You're rolling across Mars when you unexpectedly uncover some unusually light soil. You stop. You turn. You return to inspect the soil and find out it is almost purely silica -- the main ingredient in quartz and glass. Such soil has never been found on Mars before. What created this soil? Since you are the robotic rover Spirit currently rolling across Mars, you send the images and data back to Earth for analysis. Your scientist friends from the blue water planet say that such soil on Earth is usually created by either volcanic steam or a hot spring. The second hypothesis in particular indicates, once again, a wet past for part of Mars, as possibly hot water saturated with silica deposited the white soil. Intriguingly, on Earth, living microbes typically flourish under either condition. Pictured above, the uncovered light soil is visible on the right.

APOD: 2007 December 6 - Mars in View
Explanation: Very good telescopic views of Mars can be expected in the coming weeks as the Red Planet nears opposition on December 24th. Of course, opposition means opposite the Sun in planet Earth's sky - an arrangement that occurs every 26 months for Mars. Because of Mars' more elliptical orbit, the actual date of closest approach to Earth will be December 18, when Mars will be within about 88 million kilometers of our fair planet. Situated in the constellation Gemini and rising after evening twilight, the bright, ruddy disk of Mars will reach nearly 16 arcseconds in diameter (about 1/100th the diameter of the Full Moon). In this already exceptional image taken on November 18, north is down and surface markings around the sprawling, dark, albedo feature Syrtis Major are remarkably clear. The image was recorded with a video camera and filters on a 1 meter telescope at Pic Du Midi, a mountain top observatory in the French Pyrenees. NASA launched the Phoenix lander to Mars in August, scheduled to arrive in May 2008.

APOD: 2007 October 22 - Victoria Crater on Mars
Explanation: Scroll right to see the largest crater yet visited by a rover on Mars. Reaching the expansive Victoria Crater has been a goal for the robotic Opportunity rover rolling across Mars for the past two years. Victoria crater has about five times the diameter of Endurance Crater, which Opportunity spent six months exploring. Opportunity reached Victoria last year, and was cautiously probing the edges of the stadium-sized crevice while waiting for large dust storms to clear. A safe path was found, and Opportunity has slowly entered into Victoria Crater. It is hoped that Victoria Crater will show a deep stack of layers uncovered by the initial impact, and hence new clues into the ancient surface history of Mars. Visible in the distance in the above mosaic is the far rim of Victoria Crater, lying about 800 meters away and rising about 70 meters above the crater floor. The alcove in front has been dubbed Duck Bay.

APOD: 2007 September 28 - A Hole in Mars Close Up
Explanation: In a close-up from the HiRISE instrument onboard the Mars Reconnaissance Orbiter, this mysterious dark pit, about 150 meters across, lies on the north slope of ancient martian volcano Arsia Mons. Lacking raised rims and other impact crater characteristics, this pit and others like it were originally identified in visible light and infrared images from the Mars Odyssey and Mars Global Surveyor spacecraft. While the visible light images showed only darkness within, infrared thermal signatures indicated that the openings penetrated deep under the martian surface and perhaps were skylights to underground caverns. In this later image, the pit wall is partially illuminated by sunlight and seen to be nearly vertical, though the bottom, at least 78 meters below, is still not visible. The dark martian pits are thought to be related to collapse pits in the lava flow, similar to Hawaiian volcano pit craters.

APOD: 2007 September 17 - Inside Victoria Crater on Mars
Explanation: NASA's Opportunity rover is now inside Victoria Crater on Mars. Last week the robot rolled about 20 meters into the largest crater any Martian rover has yet encountered, the crater next to which Opportunity has been perched for months. Currently, the rolling explorer is situated in Duck Bay alcove, peering across at the internal crater wall dubbed Cape St. Vincent. The above wide-angle view is from Opportunity's front hazard-identification camera. Over the next few weeks, Opportunity is scheduled to explore this telling alien indentation, searching for clues to the ancient past of Mars before the huge impact that created Victoria Crater ever took place.

APOD: 2007 August 28 - Could Hydrogen Peroxide Life Survive on Mars
Explanation: Is there life on Mars? Although no unambiguous evidence for indigenous life on Mars has ever been found, a more speculative question -- could some life forms survive on Mars -- has taken on a new twist. Two planetary scientists recently speculated that were extremophile microbes to involve a mixture of hydrogen peroxide (H2O2) and water (H2O), these microbes might well be able survive the thin, cold, dry atmosphere on Mars. Life that involves hydrogen peroxide does exist here on Earth, they note, and such life would be better able to absorb water on Mars. They also claim that such life would be consistent with the ambiguous results coming out from the life-detecting experiments aboard the old Viking Landers. Although such speculation is not definitive, debating possibilities for life on Mars has again proven to be fun and a magnet for media attention. Pictured above, the Viking Lander 2 captured an unusual image of the Martian surface in 1979 sporting a thin layer of seasonal water ice.

APOD: 2007 August 8 - Phoenix Rises Toward Mars
Explanation: Can Mars sustain life? To help answer this question, last week NASA launched the Phoenix mission to Mars. In May 2008, Phoenix is expected to land in an unexplored north polar region of Mars that is rich in water-ice. Although Phoenix cannot move, it can deploy its cameras, robotic arm, and a small chemistry laboratory to inspect, dig, and chemically analyze its landing area. One hope is that Phoenix will be able to discern telling clues to the history of ice and water on Mars. Phoenix is also poised to explore the boundary between ice and soil in hopes of finding clues of a habitable zone there that could support microbial life. Phoenix has a planned lifetime of three months on the Martian surface.

APOD: 2007 August 5- The Dotted Dunes of Mars
Explanation: What causes the black dots on dunes on Mars? As spring dawned on the Northern Hemisphere of Mars in 2004, dunes of sand near the poles begin to defrost. Thinner regions of ice typically thaw first revealing sand whose darkness soaks in sunlight and accelerates the thaw. The process might involve sandy jets exploding through the thinning ice. By summer, the spots expanded to encompass the entire dunes that were then completely thawed and dark. The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas. Taken in mid-July, the above image shows a field of spotted polar dunes spanning about 3 kilometers near the Martian North Pole. Today, the future of Mars rovers Spirit and Opportunity remains unknown windy dust storms continue to starve them of needed sunlight.

APOD: 2007 July 1 - Steep Cliffs on Mars
Explanation: Vertical cliffs of nearly two kilometers occur near the North Pole of Mars. Also visible in the above image of the Martian North Polar Cap are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash. The cliffs are thought to border volcanic caldera. Although the sheer drop of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System, including the 3.4-kilometer depth of Colca Canyon on Earth and the 20 kilometer depth of Verona Rupes on Uranus' moon Miranda. The above image, digitally reconstructed into a perspective view, was taken by the High Resolution Stereo Camera on board the ESA's robotic Mars Express spacecraft currently orbiting Mars.

APOD: 2007 May 28 - A Hole in Mars
Explanation: Black spots have been discovered on Mars that are so dark that nothing inside can be seen. Quite possibly, the spots are entrances to deep underground caves capable of protecting Martian life, were it to exist. The unusual hole pictured above was found on the slopes of the giant Martian volcano Arsia Mons. The above image was captured three weeks ago by the HiRISE instrument onboard the Mars Reconnaissance Orbiter currently circling Mars. The holes were originally identified on lower resolution images from the Mars Odyssey spacecraft, The above hole is about the size of a football field and is so deep that it is completely unilluminated by the Sun. Such holes and underground caves might be prime targets for future spacecraft, robots, and even the next generation of human interplanetary explorers.

APOD: 2007 April 21 - 3D Face on Mars
Explanation: Get out your red/blue glasses and gaze down on this weathered mesa on Mars. Of course, described as a rock formation that resembles a human head in a 1976 NASA press release, this mesa is also famous as the Face on Mars. The sharp stereo image was created by combining high resolution pictures from cameras on two different spacecraft in Mars orbit - Mars Reconnaissance Orbiter and Mars Global surveyor. It shows rugged details of the approximately 2 kilometer wide, isolated hill - similar to mesa landforms on planet Earth - rising some 240 meters above the plains of the martian Cydonia region. This remarkable 3D view exaggerates the hill's vertical dimensions.

APOD: 2007 March 13 - Attacking Mars
Explanation: The Spirit rover attacked Mars again in 2005 September. What might look, above, like a military attack, though, was once again just a scientific one - Spirit was instructed to closely inspect some interesting rocks near the summit of Husband Hill. Spirit's Panoramic Camera captured the rover's Instrument Deployment Device above as moved to get a closer look at an outcrop of rocks named Hillary. The Spirit rover, and its twin rover Opportunity, have now been exploring the red planet for over three years. Both Spirit and Opportunity have found evidence that parts of Mars were once wet.

APOD: 2006 December 12 - Light Deposits Indicate Water Flowing on Mars
Explanation: What's creating light-toned deposits on Mars? Quite possibly -- water! Images of the same parts of mid-latitude Mars taken over the years but released only last week have shown unexpected new light-toned deposits where there were none before. One clear case is shown above, where the same crater on Mars is shown as photographed in 1999 August and again in 2005 September. The unusual deposit is visible only on the more recent photograph. Apparent tributaries near the bottom bolster the leading hypothesis that water gushed out of the crater wall, flowed down the crater, and soon evaporated into the thin Martian atmosphere. Although frozen water-ice has been known near the Martian poles for years, free flowing surface water like this was not expected to be seen in the mid-latitudes of Mars. If confirmed, such water springs might make more of Mars hospitable to life and human visitation than previously believed.

APOD: 2006 December 6 - Spirit Rover on Mars Imaged from Orbit
Explanation: If you have the right equipment, you can see the Spirit rover currently rolling across Mars. The right equipment, however, is currently limited to the High Resolution Imaging Science Experiment onboard the Mars Reconnaissance Orbiter (MRO). MRO arrived at Mars in March and just started science observations of the red planet last month. Visible in the above spectacularly high resolution image is the Spirit rover in the Columbia Hills of Mars. Objects as small as one meter are resolved. Also visible are the tracks made by the robot explorer and a large plateau of layered rock dubbed Home Plate. MRO will continue to image the red planet in unprecedented detail, creating images that will likely be important in better understanding the geology and weather on Mars, as well as indicating good candidate landing sites for future missions to Mars.

APOD: 2006 December 3 - Phobos: Doomed Moon of Mars
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Express spacecraft, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: 2006 November 1 - McMurdo Panorama from Mars
Explanation: This was Spirit's view on Martian-day 1,000 of its 90-Martian-day mission. The robotic Spirit rover has stayed alive so long on Mars that it needed a place to wait out the cold and dim Martian winter. Earth scientists selected Low Ridge hill, a place with sufficient slant to give Spirit's solar panels enough sunlight to keep powered up and making scientific observations. From its Winter Haven, Spirit has been able to build up the above 360-degree panorama, which has been digitally altered to exaggerate colors and compressed horizontally to fit your screen. The long winter is finally ending in the south of Mars, and with the increasing sunlight plans are now being made for Spirit to further explore the rocky Columbia Hills inside intriguing Gusev crater.

APOD: 2006 October 17 - Clouds and Sand on the Horizon of Mars
Explanation: If you could stand on Mars -- what might you see? Like the robotic Opportunity rover rolling across the red planet, you might well see vast plains of red sand, an orange tinted sky, and wispy light clouds. The Opportunity rover captured just such a vista after arriving at Victoria Crater earlier this month, albeit in a completely different direction from the large crater. Unlike other Martian vistas, few rocks are visible in this exaggerated color image mosaic. The distant red horizon is so flat and featureless that it appears similar to the horizon toward a calm blue ocean on Earth. Clouds on Mars can be composed of either carbon dioxide ice or water ice, and can move quickly, like clouds move on Earth. The red dust in the Martian air can change the sky color above Mars from the blue that occurs above Earth toward the red, with the exact color depending on the density and particle size of the floating dust particles.

APOD: 2006 October 9 - Mars Rover at Victoria Crater Imaged from Orbit
Explanation: An unusual spot has been found on Mars that scientists believe is not natural in origin. The spot appears mobile and is now hypothesized to be a robot created by an intelligent species alien to Mars. In fact, the spot appears to be NASA's robotic Opportunity rover currently rolling across Mars. The ability to see the Martian rover from orbit has recently been demonstrated by the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter (MRO). The new spacecraft achieved orbit around Mars in 2006 March. Last week, MRO imaged the location of Victoria Crater and the rover Opportunity that had just arrived there. In the above image at spectacularly high resolution, objects about one meter in size are resolved, and this includes the rolling rover. Such images may help scientists better determine if any safe path exists for Opportunity to enter large crater. In the inset image on the upper left, the whole of Victoria Crater was also imaged by MRO.

APOD: 2006 October 2 - Victoria Crater on Mars
Explanation: Scroll right to see the largest crater yet visited by a rover on Mars. Reaching the expansive Victoria Crater has been a goal for the robotic Opportunity rover rolling across Mars for the past 21 months. Opportunity reached Victoria last week, and is cautiously probing the stadium-sized crevice. It is hoped that Victoria Crater will show a deep stack of layers uncovered by the initial impact, and hence new clues into the ancient surface history of Mars. Visible in the distance of the above image mosaic is the far rim of Victoria Crater, lying about 800 meters away and rising about 70 meters above the crater floor. The alcove in front has been dubbed Duck Bay. Victoria crater has about five times the diameter of Endurance Crater, which Opportunity spent six months exploring. If a safe path is found, Opportunity may actually attempt to enter Victoria Crater.

APOD: 2006 September 26- Mars Express: Return to Cydonia
Explanation: The unusual stone mesas of the Cydonia region on Mars are quite striking in appearance. Last week, the Mars Express project released a new close-up image of a portion of the Cydonia region on Mars. This new image, taken by the robotic Mars Express spacecraft now orbiting Mars, shows an area about 90 kilometers wide. In the far lower right of the above image, a particularly picturesque mesa can be seen as the upper right of the two mesas visible there. This mesa, when lit from just the right sun angle, can appear similar to a human face and became famous as the Face on Mars in 1976 Viking orbiter images. Better images show it to be just an interesting mesa. Such complex looking landforms in the Cydonia region are thought to be the result of landslides and erosion of the ancient Martian crust.

APOD: 2006 September 25 - Mars Express Close Up of the Face on Mars
Explanation: Wouldn't it be fun if clouds were turtles? Wouldn't it be fun if the laundry on the bedroom chair was a friendly monster? Wouldn't it be fun if rock mesas on Mars were faces or interplanetary monuments? Clouds, though, are small water droplets, floating on air. Laundry is cotton, wool, or plastic, woven into garments. Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly, as the above recently-released digital-perspective image shows. Is reality boring?

APOD: 2006 August 23 - Sandy Gas Jets Hypothesized on Mars
Explanation: What's causing seasonal dark spots on Mars? Every spring, strange dark spots appear near the Martian poles, and then vanish a few months later. These spots typically span 50 meters across and appear fan shaped. Recent observations made with THEMIS instrument onboard NASA's Mars Odyssey, currently orbiting Mars, found the spots to be as cold as the carbon dioxide (CO2) ice beneath them. Based on this evidence, a new hypothesis has been suggested where the spots are caused by explosive jets of sand-laden CO2. As a pole warms up in the spring, frozen CO2 on the surface thins, perforates, and begins to vent gaseous CO2 held underneath. Within this hypothesis, interspersed dark sand would explain the color of the spots, while the underlying frozen CO2 would explain the coolness of the spots. Pictured above, an artist depicts what it might be like to stand on Mars and witness the venting of these tremendous gas and dust jets.

APOD: 2006 July 3 - The View toward Husband Hill on Mars
Explanation: This Martian vista is only part of one of the greatest panoramic views of Mars that has ever been attempted. The expansive mosaic is helping to keep the robotic Spirit rover busy over the energy draining winter in the southern hemisphere of Mars. During the winter, Spirit is constrained to stay on the side of McCool Hill in order to keep its solar panels pointed toward the Sun. The panorama has so far involved over 800 exposures, very little digital compression, and will take over a month to complete. The view shown is toward Husband Hill, a hill that Spirit climbed last year. A careful inspection of the above image shows tracks crossing from the center to the right.

APOD: 2006 June 5 - The Road to Victoria Crater on Mars
Explanation: Here is a road never traveled. To get to Victoria Crater on Mars, the rolling robotic rover Opportunity must traverse the landscape shown above. Victoria Crater lies about one kilometer ahead. The intervening terrain shows a series of light rock outcrops that appears like some sort of cobblestone road. Surrounding this naturally-occurring Martian road, is Martian sand ripples that must be navigated around. Inspection of the outcrop road shows it to be sprinkled with many small round rocks dubbed blueberries. Opportunity and its sister robot Spirit continue their third year exploring Mars. Within the next month, planetary scientists hope to maneuver Opportunity across Meridiani Planum to get a good view of 800-meter diameter Victoria Crater.

APOD: 2006 May 15 - Volcanic Bumpy Boulder on Mars
Explanation: What created this unusually textured rock on Mars? Most probably: a volcano. Dubbed Bumpy Boulder, the strange stone measuring just under a half-meter high was found by the robotic Spirit rover currently rolling across Mars. Pits on the ragged rock are likely vesicles and arise from hot gas bubbling out of hot rock ejected by an active Martian volcano. Several similar rocks are visible near Bumpy Boulder that likely have a similar past. The above true-color image was taken about one month ago. The Spirit rover, now in its third year of operation on Mars, is weathering the low sunlight winter of Mar's northern hemisphere on a hillside slope in order to maximize the amount of absorbable battery-refreshing sunlight.

APOD: 2006 April 22 - Z is for Mars
Explanation: This composite of images spaced about a week apart - from late July 2005 (bottom right) through February 2006 (top left) - traces the retrograde motion of ruddy-colored Mars through planet Earth's night sky. On November 7th, 2005 the Red Planet was opposite the Sun in Earth's sky (at opposition). That date occurred at the center of this series with Mars near its closest and brightest. But Mars didn't actually reverse the direction of its orbit to trace out the Z-shape. Instead, the apparent backwards or retrograde motion with respect to the background stars is a reflection of the motion of the Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, the Earth moving more rapidly through its own relatively close-in orbit. The familiar Pleiades star cluster lies at the upper left.

APOD: 2006 April 19 - Mars and the Star Clusters
Explanation: This evening's skyscape includes a view similar to this one, recorded in western skies on April 16 - an orange-hued planet Mars wandering near rich open star cluster M35. Also notable is fainter star cluster NGC 2158, just above and left of M35. The grouping appears near the "foot stars" of the constellation Gemini, but of course Mars is in the foreground, just over 14 light-minutes from planet Earth. The hundreds of stars in cluster M35 are more like 3,000 light-years distant. NGC 2158 is farther still, about 16,000 light-years away and is much more compact than M35. The color image shows off the contrast between hot blue stars and cooler yellowish stars within the confines of M35. But the stars of NGC 2158 are much older, and that cluster's light is definitely dominated by the orange glow of cool giant stars, making an interesting visual comparison to ruddy-colored Mars.

APOD: 2006 April 10 - Mars: The View from HiRISE
Explanation: HiRISE - the High Resolution Imaging Science Experiment - rides on the Mars Reconnaissance Orbiter (MRO)spacecraft just arrived in Mars orbit on March 10. This sharp view of the martian surface from the HiRISE camera includes image data with a full resolution of about 2.5 meters per pixel - recorded from a range of 2,500 kilometers. In the coming months, MRO's orbit will be circularized through repeated passages into Mars' outer atmosphere, a process known as aerobraking, shrinking its orbit to an altitude of only 280 kilometers. At that distance, the HiRISE experiment should be able to image the Red Planet's surface at a resolution of 28 centimeters (11 inches) per pixel. In this first color image, the false colors represent HiRISE's visible and infrared imaging data combined. The picture is nearly 24 kilometers wide and covers an area in the Bosporos Planum region of southern Mars.

APOD: 2006 April 6 - Unusual Bright Soil on Mars
Explanation: What is this bright soil on Mars? Several times while rolling across Mars, the treads of the robotic rover Spirit have serendipitously uncovered unusually bright soil. Spirit uncovered another batch unexpectedly last month while rolling toward its winter hibernation location on McCool Hill. The physics and chemistry instruments on Spirit have determined the soil, shown above, contains a high content of salts including iron-bearing sulfates. A leading hypothesis holds that these salts record the presence of past water, with the salts becoming concentrated as the water evaporated.

APOD: 2006 March 25 - Northern Spring on Mars
Explanation: Astronomical spring came to planet Earth's northern hemisphere this week (and autumn to the south) with the equinox on March 20th. But on Mars, northern spring began on January 22nd. Still in northern springtime, the Red Planet currently has a similar appearance to this composite of images from previous years taken by the long-lasting Mars Global Surveyor spacecraft. The sprawling dark region near picture center is Syrtis Major, with the whitish Hellas impact basin just below, in the southern hemisphere. The four seasons on Earth each last about 90 earth days, while Mars' larger and more eccentric elliptical orbit results in seasons that are longer and vary more widely in length - from about 140 to 190 martian sols.

APOD: 2006 March 15 - McCool Hill on Mars
Explanation: You can make it. Winter is rapidly advancing on the southern hemisphere on Mars, and the lack of sunlight could be dangerous unless you find a good place to hibernate. There it is ahead: McCool Hill. As the robotic Spirit rover rolling across Mars, you are told that this will be a good place to spend the Martian winter. On the north slope of McCool Hill, you can tilt your solar panels toward the Sun enough to generate the power you need to keep running through the winter. Between you and McCool Hill is an unusual reddish outcropping of rocks. Also visible above, unusual layered rocks lie to your right, while other scattered rocks appear either smooth or sponge-like. Fortunately, there is still some time to explore, and the landscape before you may hold more clues to the history of ancient Mars.

APOD: 2006 January 26 - An Unusual Two Toned Rock on Mars
Explanation: How did this unusual Martian rock form? The atypical two-toned rock, visible in the lower right of the above image, was photographed a few days ago by the robotic Spirit rover currently rolling across Mars. For now, the environmental processes that created the rock remain a matter of speculation. Finding unusual rocks is not unusual for Spirit or its twin rover Opportunity, however. Over the past two years, for example, the rovers have unexpectedly discovered very small gray pebbles dubbed blueberries, and a rock out in the middle of nowhere now thought to be a meteorite. Having investigated alien terrain and having found clear evidence that part of Mars had a wet past, the Earth-launched Martian rovers are now entering their third spectacular year exploring the red planet.

APOD: 2006 January 5 - New Year Mars Panorama
Explanation: According to an Earth-based calendar, the Spirit rover spent the first day of 2006 gathering data to complete this panoramic view from Gusev crater on Mars. That day corresponded to Spirit's 710th Martian day or sol on the Red Planet. Scrolling right the view spans 160 degrees, looking up a slope and across rippled sand deposits in a dark field dubbed "El Dorado". The Spirit rover is traveling in a down hill direction after reaching the summit of Husband Hill. This month, both Spirit and Opportunity rovers will celebrate two years of Mars exploration, a remarkable achievement considering their original 90 day warranty. During that time Spirit has traveled over 3.5 miles and Opportunity over 4 miles across the Martian surface.

APOD: 2005 December 14 - A Digital Opportunity Rover on Mars
Explanation: If you could see one of the robot rovers currently rolling across Mars, what would it look like? To gain this perspective useful in planning explorations, the above synthetic image was produced digitally. Above, a digital model of the Opportunity rover was added to a real image of the inside of Endurance Crater on Mars taken earlier by Opportunity itself. The size of the six-wheeled robot was scaled to the size of the tracks that the Opportunity rover actually created. In actuality, both the Opportunity and Spirit rovers currently rolling across Mars each span about two meters and so are similar in size to a large rolling desk. Also visible in the image is dark soil, ancient light rock and numerous small gray pellets known as blueberries.

APOD: 2005 November 28 - Vista Inside Gusev Crater on Mars
Explanation: What is the geologic history of Mars? To help find out, the robot Spirit rover explored the terrain on the way up to the top of Husband Hill and took pictures along the way. Earth-bound team members later combined images from one camera with colors from another to create this semi-realistic vista from near the top of the rugged hill. Many rock faces were imaged and probed along the way. The above image captures not only a high and distant Mars inside Gusev crater, but also more of the refrigerator-sized Spirit rover than other similar vistas. Visible technology includes a wide array of energy-absorbing solar panels, a sundial, and the circular high gain communications antenna.

APOD: 2005 November 14 - Everest Panorama from Mars
Explanation: If you could stand on Mars -- what might you see? Scroll right to find out. The robotic Spirit rover currently rolling across Mars climbed to the top of hill and took a series of images that were digitally combined into a 360 degree panorama over three days early last month. Spirit was instructed to take images having the same resolution as a human with 20-20 eyesight. The full panoramic result can be found by clicking on the above image and has a level of detail unparalleled in the history of Martian surface photography. The panorama was taken from the pinnacle of Husband Hill and has been dubbed the Everest panorama, in honor of the view from the tallest mountain on Earth. Visible in Gusev Crater are rocks, rusting sand, a Martian sundial, vast plains, nearby peaks, faraway peaks, and sand drifts. In the distance, fast moving dust devils can be seen as slight apparitions of red, green, or blue, the colors of filters used to build up this natural color vista.

APOD: 2005 November 8 - The Drifts of Mars
Explanation: What would it be like to walk across Mars? The robot Opportunity rover is currently experiencing what it is like to roll across part of the red planet. It's not always easy -- the rover is being instructed to dodge the deeper drifts of dark sand. During its exploration of Erebus Crater, the rover stopped and took the above picture. Inside this part of Erebus Crater, the surface of mars is covered not only by dark sand but also light outcrops of rock. Scattered across the exposed rock are numerous small round pebbles known as blueberries . Typically smaller than marbles, these unexpected and unusual rocks likely formed by accretion in an ancient wet environment. Also visible are some strange protruding edges known as razorbacks. The above image was taken early last month.

APOD: 2005 October 28 - October Mars
Explanation: This October, Mars has become a bright, yellowish star in planet Earth's sky as it approaches oppositon, the period when Mars and Earth pass close as they orbit the Sun. How close is Mars? A mere 70 million kilometers or so, close enough to allow Earth-bound astronomers excellent views of the alluring Red Planet. For example, this series of sharp Mars images follows the development of a dust storm as the planet rotates from right to left. The telescopic views clearly show details of the martian surface, including the planet's southern ice cap (top) and hood of clouds over the north pole at the bottom edge. The dust storm itself is visible as a light yellowish band across an otherwise dark region in the southern hemisphere. Even if a telescope isn't handy, be sure to check out Mars soon. It will continue to shine brightly in the night over the coming days.

APOD: 2005 August 22 - Desolate Mars: Rub al Khali
Explanation: Sometimes on Mars, there is nothing to see but red sand. Traveling two kilometers south of Endurance Crater, the robotic rover Opportunity now exploring Mars stopped and took a 360 degree panorama of a desolate and rusted Martian landscape. The site was dubbed Rub al Khali for its similarity to a barren part of the Saudi Arabian desert on Earth. In the center of the frame, the tracks from the rover's grated wheels can be seen receding far into the distance. Near the bottom, several parts of Opportunity itself are recorded, including, on the far right, a Martian sundial. Nearly 100 images in three colors to generate the above spectacular real-color image mosaic. To display the full high-resolution image would require about 300 computer monitors -- or one good large format printer.

APOD: 2005 August 8 - Mars to Appear Normal this August
Explanation: Will Mars appear extremely close and bright later this month? No. Regardless of numerous urban legends circulating, Mars will appear relatively normal in August. October is the best month to see Mars this year. The red planet is now visible in the morning before sunrise. As Earth catches up to Mars in their respective orbits around the Sun, Mars will keep rising earlier in the night. On 2005 October 30, Earth will have caught up to Mars and the planets will be the nearest to each other in their orbits -- this time around. On October 30, Mars will be nearly opposite to the Sun, rise at sunset, set at sunrise, and appear highest and brightest around midnight. Also on October 30, Mars will appear brighter than it has in the past two years, although still over 10,000 times smaller and fainter than the full Moon. Earth will then pass Mars, and Mars will appear to fade. Pictured above, Mars is shown as it appeared 2003 August 27, when it appeared slightly brighter than it had in nearly 60,000 years. The foreground setting is in the Valley of Fire state park in Nevada, USA. The ellipticity of orbits primarily determines the closeness and brightness of Mars during opposition.

APOD: 2005 April 12 - Earth or Mars?
Explanation: Which image is Earth, and which is Mars? One of the above images was taken by the robot Spirit rover currently climbing Husband Hill on Mars. The other image was taken by a human across the desert south of Morocco on Earth. Both images show vast plains covered with rocks and sand. Neither shows water or obvious signs of life. Each planet has a surface so complex that any one image does not do that planet justice. Understanding either one, it turns out, helps understand the other. Does the one on the left look like home? Possibly not, but it is Earth.

APOD: 2005 April 1 - Water on Mars
Explanation: Can you help discover water on Mars? Finding water on different regions on Mars has implications for understanding its complex geologic history, the possible existence of past life and the sustenance of potential future astronauts. Many space missions have taken photographs of the surface of the red planet, and some of them might show a subtle clue pointing to water on Mars that has been missed. By close inspection of images, following curiosity, applying scientific principles, applying knowledge about features on the Martian surface, and applying principles of planetary geology, such clues might be brought to light. In the meantime, happy April Fool's Day from the folks at APOD!

APOD: 2005 March 23 - A Dust Devil Swirling on Mars
Explanation: What is that wisp on the horizon? Scientists think that the slight white apparition is actually a Martian dust devil that was caught swirling across Mars. The above image was taken earlier this month by the robotic rover Spirit. The swirling cloud was found by comparing the above image to a previous image of the same area. Fresh dust devil tracks have been seen on Mars before, but actually seeing one up close was a surprise. The most similar phenomena to Martian dust devils on Earth are terrestrial dust devils, tornadoes and waterspouts. The ultimate cause of Martian dust devils remains unknown, but might be related to rising air heated by sun-warmed rocks and soil. Just the previous day, Spirit's power acquisition increased unexpectedly, possibly the result of a dust devil passing near or over the Spirit rover and effectively cleaning its solar panels.

APOD: 2005 March 15 - Steep Cliffs on Mars
Explanation: Vertical cliffs of nearly two kilometers occur near the North Pole of Mars. Also visible in the above image of the Martian North Polar Cap are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash. The cliffs are thought to border volcanic caldera. Although the sheer drop of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System, including the 3.4-kilometer depth of Colca Canyon on Earth and the 20 kilometer depth of Verona Rupes on Uranus' moon Miranda. The above image, digitally reconstructed into a perspective view, was taken by the High Resolution Stereo Camera on board the ESA's robotic Mars Express spacecraft currently orbiting Mars.

APOD: 2005 February 28 - Unusual Plates on Mars
Explanation: What are those unusual plates on Mars? A leading current interpretation holds that they are blocks of ice floating on a recently frozen sea covered by dust. The unusual plates were photographed recently by the European Space Agency's Mars Express spacecraft currently orbiting Mars. Oddly, the region lies near the Martian equator and not near either of Mars' frozen polar caps. Without being covered by dust, any water or ice near away from the poles would quickly evaporate right into the atmosphere. Evidence that the above-imaged plates really are dust-covered water-ice includes a similarity in appearance to ice blocks off Earth's Antarctica, nearby surface fractures from which underground water could have flowed, and the shallow depth of the craters indicating that something is filling them in. If correct, the low abundance of craters indicates that water may have flowed on Mars as recently as five million years ago.

APOD: 2005 February 9 - Heat Shield Impact Crater on Mars
Explanation: Broken metal and scorched Mars make the impact site of Opportunity's heat shield one of the more interesting sites inspected by the rolling robot. Visible on the image left is the conical outer hull of the shattered heat shield expelled by Opportunity as it plummeted toward Mars last year. Scrolling right will show not only another section of the heat shield but the impact site itself. The site is of interest partly because its creation was relatively well understood. The impact splattered subsurface light red dirt, while a darker material appears to track toward the large debris. Behind the impromptu space exhibit lies a vast alien landscape of featureless plains and rust-tinted sky.

APOD: 2005 January 21 - Metal on the Plains of Mars
Explanation: What has the Opportunity rover found on Mars? While traversing a vast empty plain in Meridiani Planum, one of Earth's yearling rolling robots found a surprise when visiting the location of its own metallic heat shield discarded last year during descent. The surprise is the rock visible on the lower left, found to be made mostly of dense metals iron and nickel. The large cone-shaped object behind it -- and the flank piece on the right -- are parts of Opportunity's jettisoned heat shield. Smaller shield debris is also visible. Scientists do not think that the basketball-sized metal "Heat Shield Rock" originated on Mars, but rather is likely an ancient metallic meteorite. In hindsight, finding a meteorite in a vast empty dust plain on Mars might be considered similar to Earth meteorites found on the vast empty ice plains of Antarctica. The finding raises speculations about the general abundance of rocks on Mars that have fallen there from outer space.

APOD: 2004 December 15 - Looking Back Over Mars
Explanation: Pictured above, the path of the robot rover Spirit on Mars can be traced far into the distance. Spirit has now crossed kilometers of plains covered with rocks and sand, approached the lip of a crater 200-meters across, and climbed a series of hills. Spirit's path has been not only one of adventure but discovery. Landing inside vast Gusev crater near the beginning of this year, Spirit, along with its sister robot Opportunity across the planet, has uncovered key evidence for ancient Martian water. The recent discovery of goethite, a mineral only known to form on Earth in the presence of water, bolsters the case. Spirit and Opportunity continue to roam the red planet in search of different and more detailed clues to the unfolding ancient past of Mars.

APOD: 2004 November 19 - Phobos: Doomed Moon of Mars
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The largest moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning new color image from the Mars Express spacecraft, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: 2004 September 22 - Spirit Rover at Engineering Flats on Mars
Explanation: Is it art? Here the paintbrush was the Spirit robotic rover, the canvas was the soil on Mars, and the artists were the scientists and engineers of the Mars Exploration Rover Mission. The picture created was mostly unintentional -- the MERS team was primarily instructing Spirit to investigate rocks in and around Hank's Hollow in a location called Engineering Flats on Mars. After creating the ground display with its treads, the Spirit rover was instructed to photograph the area along with itself in silhouette. Both Mars rovers, Spirit and Opportunity, are now back in contact after an expected radio blackout caused by Mars moving behind the Sun. NASA has also announced that it is extending the rovers missions for six months, so long as they keep working.

APOD: 2004 September 4 - Neutron Mars
Explanation: Looking for water on Mars, researchers using detectors on board the orbiting Mars Odyssey spacecraft have created this false-color global map of energetic neutrons from the otherwise Red Planet. What do neutrons have to do with water? As cosmic rays from interplanetary space penetrate the thin martian atmosphere and reach the surface they interact with elements in the upper layer of soil, scattering neutrons back into space. But if the martian soil contains hydrogen, it seriously absorbs energetic scattered neutrons. Tracking variations in absorption, neutron detectors can map changes in surface hydrogen content from orbit. Hydrogen content is taken as a surrogate measure of frozen water (H20), the most likely form of hydrogen close to the martian surface. Thus, bluer shades in the above map correspond to larger presumed concentrations of near-surface water ice. Water ice at the martian poles came as no surprise, but significant concentrations also seem to be present at lower latitudes. The melting of such near-surface ice could be responsible for the formation of martian gullies.

APOD: 2004 August 31 - The Dotted Dunes of Mars
Explanation: What causes the black dots on dunes on Mars? As spring dawns on the Northern Hemisphere of Mars, dunes of sand near the poles begin to defrost. Thinner regions of ice typically thaw first revealing sand whose darkness soaks in sunlight and accelerates the thaw. By summer, the spots will have expanded to encompass the entire dunes that will then be completely thawed and dark. The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas. Taken in mid-July, the above image shows a field of spotted polar dunes spanning about 3 kilometers near the Martian North Pole. Meanwhile, in the Southern Hemisphere of Mars, the Earth-sent robot Martian rovers will try to survive through Martian winter, which peaks in mid-September.

APOD: 2004 August 23 - Looking Out Over Mars
Explanation: What would it be like to climb a hill and look out over Mars? That opportunity was afforded the Spirit rover earlier this month as it rolled to a high perch in the Columbia Hills. Peering out, the rolling robot spied the interior plains and distant rim of Gusev Crater, beyond an outcrop of rocks called Longhorn. Spirit continues to find evidence that many rock shapes have been altered by ancient water. Both Spirit and her sister robot Opportunity have completed their primary three-month mission but remain in good enough condition to continue to explore Mars.

APOD: 2004 July 14 - Polar Polygons on Mars
Explanation: What's the best way to the city center? What looks like a street map of some city on Earth is actually a series of naturally-formed fragmented polar polygons on Mars. The existence of polar polygons on Mars is particularly interesting as they may indicate regions where water ice lies within a few meters of the surface. Similar looking polygons are commonly found in the arctic and Antarctic of Earth, where they typically form from a repetitive cycle of freezing and thawing. The above image spans a distance of about 3 kilometers and was taken recently by the orbiting Mars Global Surveyor.

APOD: 2004 June 28 - Spirit Rover Reaches the Columbia Hills on Mars
Explanation: The Spirit robotic rover on Mars has now reached the Columbia Hills on Mars. Two of the hills are shown on approach near the beginning of June. The above true-color picture shows very nearly what a human would see from Spirit's vantage point. The red color of the rocks, hills, and even the sky is caused by pervasive rusting sand. Spirit has now traveled over 3 kilometers since it bounced down onto the red planet in January. The robotic explorer, controlled and programmed remotely from Earth, is now investigating a rock called Pot of Gold. On the other side of Mars, Spirit's twin Opportunity is now inspecting unusual rocks inside a pit dubbed Endurance crater.

APOD: 2004 May 19 - Brain Crater on Mars
Explanation: What caused this unusual looking crater floor on Mars? Appearing at first glance to resemble the human brain, the natural phenomena that created the unusual texture on the floor of this Martian impact crater are currently under investigation. The light colored region surrounding the brain-textured region is likely sand dunes sculpted by winds. The Mars Global Surveyor robot spacecraft that has been orbiting Mars since 1997 took the above image. Meanwhile, down on the surface, robots Spirit and Opportunity continue to roll, inspecting landscape, rocks, and soil for clues to the ancient watery past of the red planet. Humorously, this brain-terrain on Mars spans about a kilometer, making it just about the right size to fit inside the rock formation once dubbed the Face on Mars.

APOD: 2004 May 10 - Endurance Crater on Mars
Explanation: Scroll right to see the inside of Endurance Crater, the large impact feature now being investigated by the Opportunity rover rolling across Mars. The crater's walls show areas of light rock that might hold clues about the ancient watery past of this Martian region. Inspection of this true-color image shows, however, that much of this interesting rock type is confined to crater walls that might be hard for even this wily robot to access. Both of the Mars rovers have now successfully completed their original mission and are now exploring topical opportunities.

APOD: 2004 May 4 - Missoula Crater on Mars
Explanation: Scroll right to see the rocks, craters, and hills that were in view for the Spirit rover last week as it continued its trek across Mars. Missoula crater, taking up much of the above frame, appeared from orbit to have ejecta from Bonneville crater inside it. Upon closer inspection, however, Spirit finds only evidence for wind-blown drifts. The rocks show numerous blisters and small cavities that may have occurred as ancient water vapor evaporated from hot cooling lava. Columbia Hills in the distance is now planned as the ultimate destination for the Spirit rover. Both of the Mars rovers have now successfully completed their original mission and are now exploring topical opportunities.

APOD: 2004 April 1 - April Fools Day More Intense On Mars
Explanation: Today, April 1st, astrophysicists have announced a surprising discovery - April Fools Day is more intense on Mars! Though the discovery is contrary to accepted theories of April Fools Day, researchers note that there are several likely causes for the severe martian April Fools phenomenon. For starters, gravity, the force that opposes comedy throughout the universe, is only about 3/8ths as strong on Mars' surface as it is on planet Earth. Also, a martian day, called a sol, lasts nearly 40 minutes longer than an earth day. And furthermore ... well, as soon as they think of some more reasons, they've promised to tell us. Happy April Fools day from the editors at APOD! Editors note: Mars rover Spirit recorded this image looking out toward the eastern horizon and the Columbia Hills over 2 kilometers in the distance. Its journey across this rocky martian terrain could take from 60 to 90 sols.

APOD: 2004 March 3 - Opportunity Rover Indicates Ancient Mars Was Wet
Explanation: Was Mars ever wet enough to support life? To help answer this question, NASA launched two rover missions to the red planet and landed them in regions that satellite images indicated might have been covered with water. Yesterday, mounting evidence was released indicating that the Mars Opportunity rover had indeed uncovered indications that its landing site, Meridiani Planum, was once quite wet. Evidence that liquid water once flowed includes the physical appearance of many rocks, rocks with niches where crystals appear to have grown, and rocks with sulfates. Pictured above, Opportunity looks back on its now empty lander. Visible is some of the light rock outcropping that yielded water indications, as well as the rim of the small crater where Opportunity landed. The rover will continue to explore its surroundings and try to determine the nature and extent that water molded the region.

APOD: 2004 February 25 - White Boat Rock on Mars
Explanation: What caused this rock to have an unusual shape? Earlier this month the robot Spirit rover on Mars stopped to examine a rock dubbed "white boat", named for its unusually light color and shape. White boat, the large rock near the image center of the above color-composite image, was examined by Spirit just after Adirondack, a football-sized rock determined to be composed of volcanic basalt. Spirit resumed scientific operations two weeks ago after recovering from a computer memory problem. Spirit and its twin rover Opportunity, on the other side of Mars, continue to roam the red planet in search of clues to the ancient past of Earth's most hospitable neighbor.

APOD: 2004 February 16 - A Patch of Spherules on Mars
Explanation: Some patches of Mars are full of mysterious tiny spherules. The microscopic imager on board the Opportunity rover on Mars recorded, last week, the above image showing over a dozen. The image was taken near a rock outcrop called Stone Mountain and spans roughly 6 centimeters across. A typical diameter for one of the pictured spherules is only about 4 millimeters, roughly the size of a small blueberry. The spherules appear to be much grayer and harder than surrounding rock. Debate rages on the origin of the tiny spherules, and whether their shape has to do with a slow accumulation of sediments suspended in water, or flash-frozen rock expelled during a meteor impact or volcanic eruption. A layered spherule, if ever found, would favor a water-based origin. Meanwhile, Opportunity is being programmed to dig into the Martian surface of Meridiani Planum to see what is there.

APOD: 2004 February 10 - Unusual Spherules on Mars
Explanation: What are those unusual spherules on Mars? The Mars Opportunity rover has now photographed several unusual nodules on Mars that have a nearly spherical shape. Many times these spherules are embedded in larger rock outcroppings but appear grayer. Pictured in the inset is one such spherule embedded in a rock dubbed Stone Mountain, visible to the Opportunity rover now rolling inside a small crater on Meridiani Planum. Opportunity was directed to go right up to Stone Mountain to get a better look. The inset picture spans only 3 centimeters across, revealing the rock to be named more for shape than actual size. Scientists are currently debating the origin of the spherules. One leading hypothesis holds that the beads were once-molten rock that froze in mid-air after an impact or a volcanic eruption. Another hypothesis holds that the spherules are concretions, hard rock that slowly accumulates around a central core. Opportunity will work to solve this mystery and others over the next few days.

APOD: 2004 January 29 - Valles Marineris Perspective from Mars Express
Explanation: Europe's Mars Express satellite has started returning detailed color images of the red planet. The first of the current armada to arrive at Mars, the orbiting satellite will photograph the entire Martian surface to a resolution of 10 meters or higher, map the mineral composition to 100 meter resolution, and investigate the global circulation of the atmosphere. Pictured above is a 3D perspective of the first image released from this satellite -- a stunning computer reconstruction of part of the Valles Marineris region, a canyon nicknamed the Grand Canyon of Mars. In reality, Valles Marineris is four times longer and five times deeper than its Arizona counterpart. The above image shows a portion of Valles Marineris roughly 65 kilometers across, detailing many ridges and valleys. Mars Express is scheduled to continue to send back images for at least a full Martian year.

APOD: 2004 January 27 - Opportunity on Mars
Explanation: You've just woken up in a small crater on Mars. The surrounding landscape is barren, strange, and alien. You've never been on this world before. You transmit pictures that are instantly rebroadcast all over your home world. You are the eyes for billions of people. You seek adventure. Your mission is to explore this strange new world and search for signs of pre-historic life. You have six wheels, one arm, and X-ray eyes. Surrounding you, pictured above, is iron sand and light-colored protrusions that might be bedrock. You are the Opportunity Rover that landed on Mars just this past weekend.

APOD: 2004 January 24 - Valles Marineris from Mars Express
Explanation: Looking down from orbit on January 14, ESA's Mars Express spacecraft scanned a 1700 by 65 kilometer swath across Valles Marineris - the Grand Canyon of Mars - with its remarkable High Resolution Stereo Camera. This spectacular picture reconstructs part of the scanned region from the stereo colour image data recording the rugged terrain with a resolution of 12 metres per pixel. Joining Mars Global Surveyor and Mars Odyssey, Mars Express has been orbiting the red planet since December 25th, returning scientific data, acting as a communications relay, and even making coordinated atmospheric observations with NASA's Spirit rover on the surface. The Beagle 2 lander was released from Mars Express making a landing attempt also on December 25th, but no signal has been received so far.

APOD: 2004 January 21 - Adirondack Rock on Mars
Explanation: Is this a great pyramid on Mars? Actually, the pictured rock dubbed Adirondack has an irregular shape, is only about the size of a football, and has formed by natural processes. Still, its relatively large size and dust-free surface made it the first destination for the robotic Spirit rover currently roving Mars. Spirit, itself the size of a golf cart, will now attempt to determine the rock's composition and history by prodding it with its sophisticated mechanical arm. Spirit's arm, programmed remotely from Earth, has the capability to bend, grind, and photograph the rock in minute detail. Spirit's twin rover Opportunity is scheduled to land on the other side of Mars this coming weekend.

APOD: 2004 January 14 - A Mars Panorama from the Spirit Rover
Explanation: If you could stand on Mars -- what would you see? Scrolling right will reveal a full color 360-degree panoramic view from NASA's Spirit Rover that landed on Mars just 10 days ago. The image is a digital mosaic from the panoramic camera that shows the view in every direction. Annotated on the image are the directions and distances to various hills along the horizon. These hills are valuable for orienting Spirit since they are also visible to the Mars Global Surveyor and Mars Odyssey spacecraft orbiting high overhead. Visible in the foreground are several instruments and airbags around Columbia Memorial Station. Spirit will attempt to roll onto the red planet in the next few days and explore interesting features.

APOD: 2004 January 8 - The Hills of Mars
Explanation: Distant hills rise above a rocky, windswept plain in this sharp stereo scene from the Spirit rover on Mars. When viewed with red/blue glasses, the picture combines left and right images from Spirit's high resolution panoramic camera to yield a dramatic 3D perspective. The hills were estimated to lie about 2 kilometers away and be approximately 50 to 100 meters high. Along with other features of the landscape, determining their direction and distance will help pinpoint the exact location of the Spirit landing site when compared with high resolution images of the region taken from Mars orbit. Much stereo image data, allowing important estimates of three dimensional shapes, sizes, and distances, is anticipated from the rover's cameras. (Editor's note: Red/blue glasses for viewing stereo pictures can be purchased or simply constructed using red and blue plastic for filters. Try it! To view this image, the red filter is used for the left eye.)

APOD: 2004 January 4 - Spirit Rover Bounces Down on Mars
Explanation: After a seven month voyage through interplanetary space, NASA's Spirit Rover has reached the surface of the Red Planet and returned the first images from its landing site in Gusev crater! The entry, descent, and landing phase of its mission - referred to by mission planners as "Six Minutes of Terror" - began Saturday night around 8:30pm PST as Spirit entered the martian atmosphere at about 12,000 miles per hour. Depicted in the above artist's illustration, the spacecraft is in the final stages of its landing sequence, swaddled in large, protective airbags and bouncing to a soft landing on Mars. The same type of airbags were used for the Mars Pathfinder landing in 1997. Updates on Spirit's status will be posted throughout the day.

APOD: 2003 December 30 - A Dust Devil Crater on Mars
Explanation: What caused the streaks in this Martian crater? Since the above image shows streaks occurring both inside and outside the crater, they were surely created after the crater-causing impact. Newly formed trails like these presented researchers with a tantalizing martian mystery but have now been identified as likely the work of miniature wind vortices known to occur on the red planet - martian dust devils. Another example of wind processes on an active Mars, dust devils had been detected passing near the Viking and Mars Pathfinder landers. Such spinning columns of rising air heated by the warm surface are common in dry and desert areas on planet Earth. Typically lasting only a few minutes, they becoming visible as they pick up loose dust. On Mars, dust devils can be up to 8 kilometers high and leave dark trails as they disturb the bright, reflective surface dust.

APOD: 2003 December 24 - Layered Hills on Mars
Explanation: Why are some hills on Mars so layered? The answer is still under investigation. Clearly, dark windblown sand surrounds outcropping of light sedimentary rock across the floor of crater Arabia Terra. The light rock clearly appears structured into many layers, the lowest of which is likely very old. Although the dark sand forms dunes, rippled dunes of lighter colored sand are easier to see surrounding the stepped mesas. Blown sand possibly itself eroded once-larger mesas into the layered hills. Most of the layered shelves are wide enough to drive a truck around. The above image, showing an area about 3 kilometers across, was taken in October by the Mars Global Surveyor spacecraft currently orbiting Mars. Tomorrow, the first of three robot spacecraft from Earth is scheduled to arrive at the red planet.

APOD: 2003 December 18 - Express to Mars
Explanation: Hurtling toward its destination, the high resolution camera on board ESA's Mars Express spacecraft recorded this tantalizing view of the Red Planet earlier this month on December 3rd. Seen from a distance of 5.5 million kilometers, features across part of Mars' western hemisphere are bathed in sunlight. The Martian night side is also prominent from the spacecraft's perspective, a view not possible for Earthbound telescopes. Launched on an interplanetary voyage of exploration in early June, Mars Express carries with it the Beagle 2 lander, scheduled to be released from Mars Express tomorrow, December 19th. Mars Express and Beagle 2 will then continue the journey separately, but both are scheduled to reach Mars on December 25th, with Mars Express entering an elliptical orbit and Beagle 2 descending to the Martian surface. Two more invaders from Earth, NASA's Mars Exploration Rovers, will arrive in January.

APOD: 2003 December 16 - Retrograde Mars
Explanation: Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars in Earth's sky is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars as they orbit around the Sun. During the most recent such pass in August, Mars loomed particularly large and bright. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion. Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop in the sky. At the top of the loop, Earth passed Mars and the retrograde motion was the highest. Retrograde motion can also be seen for other Solar System planets. In fact, by coincidence, the dotted line to the right of the image center is Uranus doing the same thing.

APOD: 2003 December 14 - Close up of the Face on Mars
Explanation: Wouldn't it be fun if clouds were turtles? Wouldn't it be fun if the laundry on the bedroom chair were a friendly monster? Wouldn't it be fun if rock mesas on Mars were faces or interplanetary monuments? Clouds, though, are small water droplets, floating on air. Laundry is cotton, wool, or plastic, woven into garments. Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly, as the above recently released photo shows. Is reality boring?

APOD: 2003 November 12 - Mars Then and Now
Explanation: Does Mars have canals? A hot debate topic of the late 1800s, several prominent astronomers including Percival Lowell not only claimed to see an extensive system of long straight canals on Mars, but used them to indicate that intelligent life exists there. The relatively close opposition of 1894 was used to make drawings like the one digitally re-scaled on the above left. The above map was originally prepared by Eugene Antoniadi and redrawn by Lowell Hess for the book Exploring Mars, by Roy A. Gallant. In more modern times, the latest Mars opposition has allowed the Hubble Space Telescope to capture a picture of similar orientation. Comparison of the two images shows that large features were impressively recorded, but that an extensive system of long and straight canals just does not exist. Satellites orbiting Mars have now shown conclusively that the red planet does indeed have surface features similar to canals, but that these are usually smaller, curved, and less extensive than that previously claimed. Real canyon systems like Noctis Labyrinthus are most likely cracks caused by surface stress.

APOD: 2003 October 24 - Mars Moons
Explanation: This year's record close approach of Mars inspired many to enjoy telescopic views of the red planet. But while Mars was so bright it was hard to miss, spotting Mars' two diminutive moons was still a good test for observers with modest sized instruments. Mars' moons were discovered in August of 1877 by Asaph Hall at the US Naval Observatory using the large 26-inch Alvan Clark refractor. Recorded on this August 22nd, innermost moon Phobos and outermost moon Deimos are seen here against the planet's glare in a digital composite image. The picture consists of of a long exposure capturing the faint, city-sized moons and overexposing the planetary disk, combined with a well exposed image of the red planet, revealing dark markings on the surface and the white south polar cap. The images were taken by astronomer Johannes Schedler using an 11-inch Schmidt-Cassegrain telescope at his observatory in southeastern Austria. (Editor's note: For help finding Mars' moons, just put your cursor over the image.)

APOD: 2003 September 22 - Opportunity Rockets Toward Mars
Explanation: Next stop: Mars. Two months ago, the second of two missions to Mars was launched from Cape Canaveral, Florida, USA above a Boeing Delta II rocket. The Mars Exploration Rover dubbed Opportunity is expected to arrive at the red planet this coming January. Pictured above, an attached RocketCam (TM) captures Opportunity separating from lower booster stages and rocketing off toward Mars. Upon arriving, parachutes will deploy to slow the spacecraft and surrounding airbags will inflate. The balloon-like package will then bounce around the surface a dozen times or more before coming to a stop. The airbags will then deflate, the spacecraft will right itself, and the Opportunity rover will prepare to roll onto Mars. A first rover named Spirit was successfully launched on June 10 and will arrive at Mars a few weeks earlier. The robots Spirit and Opportunity are expected to cover as much as 40 metres per day, much more than Sojourner, their 1997 predecessor. Spirit and Opportunity will search for evidence of ancient Martian water, from which implications might be drawn about the possibility of ancient Martian life.

APOD: 2003 September 2 - Contemplating Mars
Explanation: Is that really another world? Thousands of people the world over lined up last week to see Mars through a telescope as the red planet and Earth passed unusually close together in their orbits around the Sun. Reviews of Mars were mixed, with some people disappointed that Mars still appeared somewhat blurry. Veteran sky gazers appeared somewhat surprised by the popularity of the phenomenon, as it seemed to many that Mars was not very much brighter than it frequently appears, and the event held little promise for real discovery. Most observers, though, appeared quietly pleased to take advantage of a unique opportunity and see such an uncommon sight. Many were awed by the simple enormity of being able to see the face of a completely different world with their own eyes. Pictured above, a youngster peered toward Mars last week at an East Antrim Astronomical Society star party at the Big Collin Picnic Area north of Belfast, Northern Ireland, UK.

APOD: 2003 August 28 - Mars Rising Behind Elephant Rock
Explanation: Yesterday, at about 10 am Universal Time, Mars and Earth passed closer than in nearly 60,000 years. Mars, noticeably red, remains the brightest object in the eastern sky just after sunset. The best views of Mars, however, will continue to be from the robot spacecraft currently orbiting Mars: the Mars Global Surveyor and the Mars Odyssey. The current pass sparked the launching of four new spacecraft toward Mars, some of which will deploy landers early next year and likely return even more spectacular views of our planetary neighbor. Pictured above, Mars was photographed rising in the southeast behind Elephant Rock in the Valley of Fire State Park, Nevada, USA.

APOD: 2003 August 27 - Big Mars from Hubble
Explanation: At about 10 am Universal Time today, Mars and Earth will pass closer than in nearly 60,000 years. Mars, noticeably red, will be the brightest object in the eastern sky just after sunset. Tonight and through much of this week, many communities around the world are running a public Mars Watch 2003 campaign, where local telescopes will zoom in on the red planet. Pictured above is an image of Mars taken just last night from the Hubble Space Telescope in orbit around the Earth. This image is the most detailed view of Mars ever taken from Earth. Visible features include the south polar cap in white at the image bottom, circular Huygens crater just to the right of the image center, Hellas Impact Basin - the large light circular feature at the lower right, planet-wide light highlands dominated by many smaller craters and large sweeping dark areas dominated by relatively smooth lowlands.

APOD: 2003 August 26 - Earth Webcam Catches Mars Rotation
Explanation: Mars won't look this good. Tonight and over the next few days, when Mars is at its closest approach to Earth in nearly 60,000 years, you might get your best view ever of our planetary neighbor. Please, though, don't expect to see this much structure, or expect to see Mars rotate so much in so brief a period. The above 20-frame movie was created from 1000 frames of a backyard webcam that were meticulously aligned, added, and digitally sequenced. Pictured, Mars appears to rotate in a time-lapse sequence, with each frame separated by 30 minutes of real time. In reality, one full Martian rotation -- a Martian day -- is only about 40 minutes longer than an Earth day. For those with access to a small telescope, here is how mars will really look.

APOD: 2003 August 24 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Recently, several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

APOD: 2003 August 19 - Mars Through a Small Telescope
Explanation: How does Mars appear through a small telescope? Viewed with the unaided eye or through a small telescope, possibly the most striking part of Mars' appearance is its red color. The color derives from rust, iron oxide, which composes perhaps 10% of the Martian soil. The oxygen that rusts the surface iron on Mars originates predominantly from carbon dioxide gas, which composes 95% of the Martian atmosphere. Mars nears its closest approach with Earth in nearly 60 millennia on August 27, the red planet continues to appear larger, brighter, and a good target for sky enthusiasts. Pictured above, Mars was captured from the Canary Islands of Spain during three days in three different orientations earlier this month. Visible through the small telescope are white polar caps of water and carbon-dioxide ice, light red areas rich in lightly colored craters, and dark red areas dominated by relatively smooth lowlands.

APOD: 2003 August 15 - Sedimentary Mars
Explanation: High-resolution imaging of an area in the Schiaparelli Basin of Mars on June 3 by the MGS Mars Orbiter camera produced this stunning example of layered formations within an old impact crater. On planet Earth, such structures would be seen in sedimentary rock -- material deposited at the bottom of ancient lakes or oceans and then subsequently weathered away to reveal the layers. With the Sun shining from the left, the central layer appears to stand above the others within the 2.3 kilometer wide crater. The crater could well have been filled with water in Mars' distant past, perhaps resting at the bottom of a lake filling the Schiaparelli impact basin. Still, such layers might also have been formed by material settling out of the windy martian atmosphere. As satellites continue to examine the martian surface from orbit, NASA's Spirit and Opportunity spacecraft will attempt to land on on Mars early next year to further explore the tantalizing history of water on the Red Planet.

APOD: 2003 August 13 - Mars Rising Behind Poodle Rock
Explanation: Have you seen Mars lately? As Earth and Mars near their closest approach in nearly 60,000 years on August 27, the red planet has begun to appear dramatically bright and show interesting details through telescopes and binoculars. Although not yet visible at sunset, Mars can be seen rising increasingly earlier in the evening. Once above the horizon, Mars is easy to spot, as it sports a distinct orange-red hue and it is the brightest object in the sky after the Sun, the nearby Moon, and Venus. After Earth overtakes Mars in their respective solar orbits, Mars will be visible right from sunset, although its historic brightness will then begin to fade. Pictured above, Mars was captured rising in the south east next to Poodle Rock in Valley of Fire State Park, Nevada, USA.

APOD: 2003 July 30 - Frosty Mountains on Mars
Explanation: What causes the unusual white color on some Martian mountains? The answer can be guessed by noticing that the bright areas disappear as springtime takes hold in the south of Mars: dry ice. Dry carbon dioxide ice sublimates directly to gas from its frozen state. The frosty mountains, named Charitum Montes, have been covered with carbon dioxide ice over the Martian winter. The serene scene pictured above is not a photograph, but rather a computationally constructed digital illusion resulting from the fusion of two color images from the Mars Orbital Camera and topographic data from the Mars Orbiter Laser Altimeter. Both instruments operate from the Mars Global Surveyor robot spacecraft currently orbiting Mars. The red planet continues to grow larger in terrestrial skies as Earth and Mars move closer to their recent-record closest approach on August 27.

APOD: 2003 July 28 - Launch of the Spirit Rover Toward Mars
Explanation: Next stop: Mars. Last month the first of two missions to Mars was launched from Cape Canaveral, Florida, USA above a Boeing Delta II rocket. Pictured above, solid fuel boosters are seen falling away as light from residual exhaust is reflected by the soaring rocket. The Mars Exploration Rover dubbed Spirit is expected to arrive at the red planet this coming January. Upon arriving, parachutes will deploy to slow the spacecraft and surrounding airbags will inflate. The balloon-like package will then bounce around the surface a dozen times or more before coming to a stop. The airbags will then deflate, the spacecraft will right itself, and the Spirit rover will prepare to roll onto Mars. The robotic Spirit is expected to cover as much as 40 meters per day, much more than Sojourner, its 1997 predecessor. Spirit will search for evidence of ancient Martian water, from which implications might be drawn about the possibility of ancient Martian life. A second rover named Opportunity was successfully launched on July 7 and will arrive at Mars a few weeks later.

APOD: 2003 July 24 - Mars at the Moon's Edge
Explanation: What was that bright "star" near the Moon last week? Mars of course, as the Red Planet wandered near the waning gibbous Moon early last Thursday morning, passing behind the lunar orb when viewed from some locations in South and Central America, the Caribbean, and Florida. The Clay Center Observatory expedition to Bonita Springs, Florida produced this evocative picture of Mars grazing the Moon's dark edge by digitally stacking and processing a series of telescopic images of the event. With the cratered Moon in the foreground, the bright planet Mars seems alarmingly close, its global scale features and white south polar cap easily visible. Already impressive, the apparent size of the martian disk will continue to grow in the coming weeks, until, on August 27, Mars reaches its closest approach to planet Earth in over 50,000 years.

APOD: 2003 July 16 - Mars' Simulated View
Explanation: When earthdweller Patrick Vantuyne wondered what his home planet's single large moon would look like if viewed from Mars on July 17, he availed himself of the JPL Solar System Simulator. Of course, when viewed from Earth on that date (tomorrow), the gibbous Moon will pass tantalizingly close to Mars for observers in North, Central, and South America and will actually pass in front of (occult) the Red Planet for some locations, including much of Florida. Vantuyne's efforts were rewarded with this remarkable simulated view of the crescent Moon against the background of a darkened Earth. From the martian vantage point, the lunar orb is seen just below the tip of the Florida peninsula at 8:05 GMT. Observers on planet Earth who want to watch the corresponding Moon/Mars show in tomorrow's predawn sky should note the viewing times for selected cities.

APOD: 2003 July 15 - Mars Rising Through Arch Rock
Explanation: Mars is heading for its closest encounter with Earth in over 50,000 years. Although Mars and Earth continue in their normal orbits around the Sun, about every two years Earth and Mars are on the same part of their orbit as seen from the Sun. When this happens again in late August, Mars will be almost as near to the Sun as it ever gets, while simultaneously Earth will be almost as far from the Sun as it ever gets. This means that now is a great time to launch your space probe to Mars. Alternatively, these next few months are a great time to see a bright red Mars from your backyard. Mars is so close that global features should be visible even through a small telescope. Look for Mars to rise about 11 pm and to remain the brightest red object in the sky until sunrise. Mars will rise increasingly earlier until its closest approach in late August. Mars was captured above rising through the Arch Rock in Valley of Fire State Park, Nevada, USA.

APOD: 2003 July 10 - Dust Storm Over Northern Mars
Explanation: Almost on cue, as Mars nears its closest approach to planet Earth in recorded history, ominous seasonal dust storms are beginning to kick up. Observers worry that the activity may presage the development of a planet wide dust storm, frustrating attempts to view Mars in the coming months, a situation similar to the Red Planet's uncooperative behavior in 2001. In this example, recorded in mid-May by the Mars Global Surveyor spacecraft camera, a dust storm the size of a continent sweeps north and east (toward the upper right) across Mars' northern Acidalia Planitia. Meanwhile, interplanetary robotic explorers Mars Express/ Beagle 2, Nozomi, and the twin Mars Exploration Rovers Opportunity and Spirit, are all bound for Mars and should arrive by early January 2004.

APOD: 2003 June 2 - The Fogs of Mars
Explanation: Fogs of clouds and dust covered parts of southern Mars during last Martian winter. Giant volcanoes, such as Ascraeus Mons, the central circular feature near the top of the image, were surrounded by large water clouds. Slightly southwest, Pavonis Mons and Arisa Mons also peeked above their water clouds. The rough terrain below center is Labyrinthus Noctis, a maze of deep troughs running over 200 kilometers long. Directly south, a large white dust storm fogs Syria Planum, a large plateau. This image mosaic was taken by the Mars Global Surveyor spacecraft currently orbiting Mars. Soon, five more Earth-launched spacecraft should arrive at the Red Planet, named for the Roman god of war.

APOD: 2003 May 26 - The Earth and Moon from Mars
Explanation: What does Earth look like from Mars? The first image of Earth from the red planet was captured earlier this month by the camera onboard the Mars Global Surveyor spacecraft currently orbiting Mars. Features visible on Earth include the Pacific Ocean, clouds, much of South America, and part of North America. Earth's Moon is visible on the upper right, with the crater Tycho brightening the lower part. Previously, Earth has been imaged from the Moon and spacecraft across the Solar System.

APOD: 2003 May 2 - Five to Mars
Explanation: Come December 2003 - January 2004, an armada of five new invaders from Earth should arrive on the shores of the Red Planet -- the Japanese ( ISAS) Nozomi orbiter, the European Space Agency's Mars Express orbiter carrying the Beagle 2 lander, and NASA's own two Mars Exploration Rovers. While Nozomi began its interplanetary voyage in 1998, the other spacecraft are scheduled for launch windows beginning this June. Clearly, earthdwellers remain intensely curious about Mars and the tantalizing possibility of past or present martian life, with these robotic missions focussing on investigating the planet's atmosphere and the search for water. This mosaic of over 100 Viking 1 orbiter images of Mars was recorded in 1980 and is projected to show the perspective seen from an approaching spacecraft at a distance of 2,000 kilometers. Exceptional views of Mars will be possible from earthbound telescopes in August and September.

APOD: 2003 April 22 - Springtime on Mars
Explanation: Vast canyons, towering volcanoes, sprawling fields of ice, deep craters, and high clouds can all be seen in this image of the Solar System's fourth planet: Mars. The orbiting robot Mars Global Surveyor spacecraft took the above mosaic of images as springtime dawned in Northern Mars in 2002 May. Sprawled across the image bottom is Valles Marinaris, a canyon three times the length of Earth's Grand Canyon, and four times as deep. On the left are several volcanoes including Olympus Mons, a volcano three times higher than Earth's Mt. Everest. At the top is the North Polar Cap made of thawing water and carbon-dioxide based ice. Swirling white clouds and circular impact craters are also visible around Mars. Two rovers will be launched to Mars this summer and should arrive in 2004 January.

APOD: 2003 April 6 - Phobos: Doomed Moon of Mars
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These Martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1978 Viking 1 orbiter image, the largest moon, Phobos, is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos orbits so close to Mars, (about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: 2003 February 21 - Melting Snow and the Gullies of Mars
Explanation: Tantalizing images of gullies on Mars have offered striking evidence for recent flows of liquid water. But Mars is too cold and its atmosphere too thin for liquid water to exist on the surface. Still a new and compelling explanation for gullies carved by liquid water was inspired by this recently released image from the Mars Odyssey spacecraft. Pictured is a section of what is likely a snow covered crater in the Martian southern hemisphere. North is at the top and the scene, illuminated from the left, is about 16 kilometers wide. Patches of smooth snow pack remain along the northern crater wall, while structures resembling the famous Martian gullies appear to be emerging as the snow cover gradually disappears, and are exposed along the crater's western (left) wall. Melting snow, running underneath the snow pack and down the crater walls would be protected from the extreme surface conditions, remaining liquid and eroding the gullies over time. Could life exist in a liquid water environment beneath the Martian snow?

APOD: 2003 February 5 - Unusual Gullies and Channels on Mars
Explanation: What could have formed these unusual channels? Inside Newton Basin on Mars, numerous narrow channels run from the top down to the floor. The above picture covers a region spanning about 1500 meters across. These and other gullies have been found on Mars in recent high-resolution pictures taken by the orbiting Mars Global Surveyor robot spacecraft. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists hypothesize that liquid groundwater can sometimes surface on Mars, erode gullies and channels, and pool at the bottom before freezing and evaporating. If so, life-sustaining ice and water might exist even today below the Martian surface -- water that could potentially support a human mission to Mars. Research into this exciting possibility is sure to continue!

APOD: 2002 December 24 - Spring Dust Storms at the North Pole of Mars
Explanation: Spring reached the north pole of Mars in May, and brought with it the usual dust storms. As the north polar cap begins to thaw, a temperature difference occurs between the cold frost region and recently thawed surface, resulting in swirling winds between the adjacent regions. In the above image mosaic from the Mars Global Surveyor spacecraft currently orbiting Mars, the white material is frozen carbon dioxide that covers much of the extreme north. The choppy clouds of at least three dust storms can be identified.

APOD: 2002 December 16 - Night and Day in Melas Chasma on Mars
Explanation: What types of terrain are found on Mars? Part of the answer comes from thermal imaging by the robot spacecraft 2001 Mars Odyssey currently orbiting Mars. The above picture is a superposition of two infrared images, a black and white image taken during Martian daylight and a false-color image taken at night. For the daytime image, dark colors mean cool temperatures, dropping from about -5 degrees Celsius to low as -35 degrees Celsius. Shadowed regions appear particularly dark, while grooved structure on the floor of Melas Chasma indicates successively overlapping landslides. In the nighttime swath, blue areas have cooled relatively quickly, indicating a composition of fine-grained dust and sand.

APOD: 2002 October 24 - Gullies on Mars
Explanation: The Gullies of Mars would probably not have been sensational enough for the title of a vintage Edgar Rice Burroughs story about the Red Planet. But it would get the attention of planetary scientists today. First identified in high resolution images of Mars recorded by the orbiting Mars Global Surveyor spacecraft, the gullies are interpreted as startling evidence that liquid water flowed across the martian surface in geologically recent times. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Still, it is thought possible that water did burst out from underground layers and remain liquid long enough to erode the gullies, while alternative explanations suggest the erosion was produced by a flowing jumble of solid and gaseous carbon dioxide. Spanning a few kilometers along the wall of an impact crater this high resolution image from Mars Global Surveyor shows typical martian gullies near the top of the crater wall giving way to sand dunes toward the crater floor. Whitish frost is visible near the top and on the dark sand dunes below. The muted colors were synthesized from wide angle image data.

APOD: 2002 October 1 - Rectangular Ridges on Mars
Explanation: What could cause rectangular ridges on Mars? As data flows in from the two spacecraft currently orbiting Mars, surface structures are seen that are not immediately understood. These structures pose puzzles that planetary geologists are eager to solve, as they might provide clues to past processes that have shaped Mars over billions of years. On the right of the above image is an unusual array of ridges first spotted in Mariner 9 data in 1972. A ridge wall runs for about 5 kilometers. Two competing progenitor theories include hardened sand dunes and once-molten rock that seeped through surface cracks and cooled. Dubbed "Inca City" for their resemblance to stone walls of an ancient Earth civilization, the new Mars Global Surveyor images now show them to be part of a larger circular pattern, indicating an origin possibly related to the impact crater. (Non-natural origin hypotheses are not invoked by conservative scientists unless clear indications exist that natural processes could not work.)

APOD: 2002 September 3 - A Dust Devil on Mars
Explanation: Does the surface of Mars change? When inspecting yearly images of the Martian surface taken by the robot spacecraft Mars Global Surveyor currently orbiting Mars, sometimes new dark trails are visible. Although originally a mystery, the culprit is now usually known to be a dust devil, a huge swirling gas-cloud with similarities to a terrestrial tornado. Pictured above, a recent image has not only captured a new dark trail but the actual dust devil itself climbing a crater wall. Dust devils are created when Martian air is heated by a warm surface and begins to spin as it rises. Dust devils can stretch 8 kilometers high but usually last only a few minutes.

APOD: 2002 August 8 - Ancient Volcanos of Mars
Explanation: Findings of ancient martian microbial fossils in meteorites and liquid water related features on Mars' surface are currently controversial issues. But one thing long established by space-based observations of the Red Planet is the presence of volcanos, as Mars supports some of the largest volcanos in the solar system. This synthetic color picture recorded in March by the Mars Global Surveyor spacecraft shows two of them, Ceraunius Tholus (leftmost) and Uranius Tholus. Found north of the Tharsis region of truly large martian volcanos, these are actually two relatively small volcanos, Ceraunius Tholus being only about the size of the Big Island of Hawaii on planet Earth. Impact craters which overlay the volcanic martian terrain indicate that these volcanos are themselves ancient and inactive. North is to the right and the scene is illuminated by sunlight from the top left. A light region of dust deposited by recent global dust storms lies on the lower left flank of Ceraunius Tholus, whose summit crater is about 25 kilometers across.

APOD: 2002 May 31 - In Chandor Chasma on Mars
Explanation: Scroll right and dive into a spectacular canyon on Mars. This daytime infrared view, recently recorded by the THEMIS camera on board the orbiting Mars Odyssey spacecraft, covers a 30 by 175 kilometer swath running along the canyon floor. The north (left) end of the scene is poised at the edge of Candor Chasma, part of the great Valles Marineris canyon system. In all about 4,000 kilometers long and up to 6 kilometers deep, Valles Marineris is roughly five times the size of the Grand Canyon on planet Earth. The THEMIS camera data was recorded in three separate infrared bands and combined to make this striking false-color image. Resulting color differences along this intricate section of martian terrain are attributed to differences in mineralogy, the chemical makeup and structure of the rocks, sediments and surface dust.

APOD: 2002 May 13 - White Rock Fingers on Mars
Explanation: What caused this unusual white rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate a more mundane origin: volcanic ash. Studying the exact color of the formation indicated the volcanic origin. The light material appears to have eroded away from surrounding area, indicating a very low-density substance consistent with the ash hypothesis. The stark contrast between the rocks and the surrounding sand is compounded by the unusual darkness of the sand. The above picture was taken with the Thermal Emission Imaging System on the Mars Odyssey spacecraft currently orbiting Mars. The image spans about 10 kilometers inside a much larger crater.

APOD: 2002 March 22 - Odyssey Over Mars
Explanation: Scroll right and journey for 300 kilometers over Terra Sirenum in the cratered highlands of southern Mars. The infrared view, 32 kilometers wide, was recently recorded by the THEMIS camera on board the orbiting Mars Odyssey spacecraft. Beginning at the north (left) edge, the scene sweeps across the floor and over the rim of Koval'sky Crater. Continuing southward (right) of the crater's rim are lava flows exhibiting fractures and numerous smaller impact craters. The infrared image was made in daylight hours, so sun-facing slopes are still warm and bright while shadowed areas are cool and dark. But rocky regions also tend to remain cooler and darker than their surroundings, likely corresponding to the dark blotchy terrain along the Koval'sky Crater floor and dark rings of rocky ejecta surrounding some of the smaller craters.

APOD: 2002 March 15 - Neutron Mars
Explanation: Looking for water on Mars, researchers using detectors on board the orbiting Mars Odyssey spacecraft have created this false-color global map of energetic neutrons from the otherwise Red Planet. What do neutrons have to do with water? As cosmic rays from interplanetary space penetrate the thin martian atmosphere and reach the surface they interact with elements in the upper layer of soil, scattering neutrons back into space. But if the martian soil contains hydrogen, it seriously absorbs energetic scattered neutrons. Tracking variations in absorption, neutron detectors can map changes in surface hydrogen content from orbit. Hydrogen content is taken as a surrogate measure of frozen water (H20), the most likely form of hydrogen close to the martian surface. Blue shades in the above map correspond to large concentrations of hydrogen, indicating in particular that the martian south polar region has a high amount of water ice near the surface.

APOD: 2001 December 13 - The South Pole of Mars
Explanation: The south pole of Mars is the bright area near the center of the detailed, subtly shaded color image above. Recorded in September of this year by the Mars Global Surveyor (MGS) spacecraft, the picture shows a region surrounding the 400 kilometer wide martian polar cap in the midst of southern hemisphere spring. During this season the ice cap, predominantly layers of frozen carbon dioxide (dry ice) plus some water ice, begins to shrink as the ices change directly from solid to gas (sublimate). Hazy clouds of ice crystals and fog, extend across the bottom of the picture and a darker, more defrosted area is visible at the upper right, near the Red Planet's night side. A wealth of MGS data has allowed changes in the extent and density of the ice cap to be tracked over time. Now, researchers are also reporting indications that, in addition to seasonal changes, overall the martian southern ice cap has been dwindling in recent years -- dramatic evidence of a changing martian climate. At the measured rate, the increasing amount of carbon dioxide released could gradually raise Mars' atmospheric pressure, doubling it over hundreds to thousands of martian years.

APOD: 2001 November 27 - Ancient Layered Rocks on Mars
Explanation: Is this a picture of Mars or Earth? Oddly enough, it is a picture of Mars. What may appear to some as a terrestrial coastline is in fact a formation of ancient layered rocks and wind-blown sand on Mars. The above-pictured region spans about three kilometers in Schiaparelli Crater. What created the layers of sediment is still a topic of research. Viable hypotheses include ancient epochs of deposit either from running water or wind-blown sand. Winds and sandstorms have smoothed and eroded the structures more recently. The "water" that appears near the bottom is actually dark colored sand. The image was taken with the Mars Global Surveyor spacecraft that has now returned over 100,000 images.

APOD: 2001 November 2 - THEMIS of Mars
Explanation: Not an ancient Greek goddess, THEMIS is modern acronese for THermal EMission Imaging System. Above is this remarkable instrument's premier infrared image of Mars, from the newly orbiting Mars Odyssey spacecraft. Taken on October 30th, the sharp infrared picture covers the indicated swath of the martian southern hemisphere and shows surface temperatures in false-colors ranging from red, a warm 0 degrees Celsius, to cool purple shades of -120 degrees C. The striking, cold circular feature is Mars' south polar ice cap. Composed of frozen carbon dioxide, the ice cap is about 900 kilometers wide and shrinking during the onslaught of southern hemisphere summer. Temperatures are also seen to drop as the bottom portion of the THEMIS image sweeps beyond the terminator or shadow line, into the martian night. A thin, light blue crescent along the upper edge of the planet is the martian atmosphere. The THEMIS image data was recorded as a test of the camera system from an altitude of about 22,000 kilometers .

APOD: 2001 October 25 - Odyssey at Mars
Explanation: After an interplanetary journey lasting 200 days, the Mars Odyssey spacecraft has entered orbit around the Red Planet. This latest success is welcome as in the past, Mars has often seemed a difficult planet to visit. Beginning with the first Soviet attempts in 1960, around 30 missions have tried while only 10 or so have gone without serious mishap. Now that Mars Odyssey has arrived, its immediate future will involve aerobraking. Cautiously dipping into the martian atmosphere, the spacecraft will gradually adjust its present wide and elliptical 20-hour orbit to a circular 2-hour orbit only 400 kilometers above the planet's surface. Then, its instruments and cameras will focus on exploring the climate and geologic history of Mars, including the search for water and evidence of life-sustaining environments. In the artist's conception above, the spacecraft with wing-like solar panels is imagined firing its rocket engine for Mars orbit insertion over terrain seen in natural and false-color.

APOD: 2001 October 17 - Mars Engulfed
Explanation: For months now, Mars has been engulfed by a great dust storm, the biggest seen raging across the Red Planet in decades. As a result, these two Hubble Space Telescope storm watch images from late June and early September offer dramatically contrasting views of the martian surface. At left, the onset of smaller "seed" storms can be seen near the Hellas basin (lower right edge of Mars) and the northern polar cap. A similar surface view at right, taken over two months later, shows the fully developed extent of the obscuring global dust storm. The storm is reported to be waning, but planet-wide effects such as the warming of the upper martian atmosphere and cooling of the surface are still being monitored daily by instruments on board the Mars Global Surveyor spacecraft. The present condition of the martian atmosphere is also important to the aerobraking Mars Odyssey spacecraft, scheduled to arrive at the Red Planet next week.

APOD: 2001 September 18 - Surrounded by Mars
Explanation: Just after landing on Mars in 1997, the robotic Mars Pathfinder main station took a quick first look around. This insurance panorama was taken even before the Sagan Memorial Station camera was raised to its two-meter-high perch. The full view is best seen by slowly scrolling to the right. The unique perspective captures many Mars Pathfinder instruments in the close foreground including a screen for judging sky illumination, communications antennae, solar panels, and two ramps leading down to the surface for the robot probe Sojourner. After taking the ramp on the right, Sojourner can be seen on the Martian surface. Visible on the surface are numerous rocks and hills that came to be better studied. The Mars Pathfinder mission went on to return 16,000 images and data that resulted in many discoveries, including evidence for warmer and wetter conditions on Mars in the past. After nearly three spectacular months exploring the surface, Mars Pathfinder dropped out of communication, likely the result of depleted battery power.

APOD: 2001 August 18 - Phobos: Doomed Moon of Mars
Explanation: Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These Martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1978 Viking 1 orbiter image, the largest moon, Phobos, is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos is doomed. Phobos orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: 2001 July 18 - Mars from Earth
Explanation: Last month, Mars and Earth were right next to each other in their orbits. Formally called opposition, the event was highlighted by a very bright Mars for skywatchers and a good photo opportunity for the Hubble Space Telescope. Above, Hubble snapped the highest resolution picture of Mars ever obtained from the Earth. Visible on Mars are ice caps over the poles in white, regions covered with sand and gravel in dark brown and orange, and large dust storms in light orange. A particularly large dust storm can be seen on the lower right pouring out of Hellas Basin. This storm has since erupted into a huge planet wide storm that continues even today. Pictures like these allow planetary astronomers to continue to compare the weather patterns of Mars and Earth. When Mars next reaches opposition in 2003, its elliptical orbit will cause it to be even 20 percent closer.

APOD: 2001 June 28 - The Topography of Mars
Explanation: Mars has its ups and downs. Visible on the above interactive topographic map of the surface of Mars are giant volcanoes, deep valleys, impact craters, and terrain considered unusual and even mysterious. Particularly notable are the volcanoes of the Tharsis province, visible on the left in (false-color) red and white, which are taller than any mountains on Earth. Just to the left of center is Valles Marineris, a canyon much longer and deeper than Earth's Grand Canyon. On the right in blue is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid. Mars has many smooth lowlands in the north, and many rough highlands in the south. This map was created by the Mars Orbital Laser Altimeter (MOLA) on board the robot Mars Global Surveyor currently orbiting Mars. MOLA measures heights on Mars by precisely determining the time it takes for a low power laser beam to bounce off the surface. Zoom in by clicking anywhere on the above map.

APOD: 2001 June 26 - All of Mars
Explanation: From pole to pole, from east to west, this is all of Mars. The above picture was digitally reconstructed from over 200 million laser altimeter measurements taken by the Mars Global Surveyor spacecraft currently orbiting Mars. The image strips Mars of its clouds and dust, and renders the whole surface visible simultaneously in its true daytime color. Particularly notable are the volcanoes of the Tharsis province, visible on the left, which are taller than any mountains on Earth. Just to the left of center is Valles Marineris, a canyon much longer and deeper Earth's Grand Canyon. On the right, south of the center, is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid. Mars has many smooth lowlands in the north, and many rough highlands in the south. Mars has just passed its closest approach to Earth since 1988 and can be seen shining brightly in the evening sky.

APOD: 2001 May 28 - Close up of the Face on Mars
Explanation: Wouldn't it be fun if clouds were turtles? Wouldn't it be fun if the laundry on the bedroom chair was a friendly monster? Wouldn't it be fun if rock mesas on Mars were faces or interplanetary monuments? Clouds, though, are small water droplets, floating on air. Laundry is cotton, wool, or plastic, woven into garments. Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly, as the above recently released photo shows. Is reality boring?

APOD: 2001 April 9 - Mars Odyssey Lifts Off for Mars
Explanation: Next stop: Mars. On Saturday the 2001 Mars Odyssey spacecraft lifted off from Cape Canaveral, Florida on a path to enter orbit around Mars in late October. Pictured above, a Delta II rocket lifted the robot spacecraft, located in the nose cone, off the launch pad, while a camera mounted on the side of the rocket took the inset picture. The Odyssey orbiter will map the locations of chemical elements and minerals, look for evidence of water, and measure the Martian radiation environment. These data will help NASA better determine whether life ever arose on Mars, better understand the climate and geology or Mars, and better plan for future human exploration. The spacecraft's name is a tribute to 2001: A Space Odyssey, an epic fictional story of future space exploration written by Arthur C. Clarke.

APOD: 2001 March 27 - Swiss Cheese Like Landscape on Mars
Explanation: Why do parts of the south pole of Mars look like swiss cheese? This little-understood landscape features flat-topped mesas nearly 4 meters high and circular indentations over 100 meters across. Since this swiss-cheese topography is unique to the polar cap covering southern Mars, exogeologists speculate that mesa composition might be high in frozen carbon dioxide (dry ice). Additionally, dry ice might have had a role in this strange landscape's creation. In the above picture, the Martian surface is illuminated by sunlight from the upper right. The above picture was taken in August 1999 by the robot Mars Global Surveyor spacecraft currently orbiting Mars.

APOD: 2001 February 26 - Sand Dunes on Mars
Explanation: Sand dunes on Mars can appear exotic. The dark dunes above might be compared to shark's teeth or chocolate confections. In reality, they arise from the complex relationship between the sandy surface and high winds on Mars. These particular dunes are located in Proctor Crater, a 170 kilometer wide crater first seen to house sand dunes by Mariner 9 more than 25 years ago. The above picture was taken by Mars Global Surveyor (MGS), a robot spacecraft currently in orbit around Mars. MGS has recently completed a primary goal of taking and transmitting detailed survey images of the red planet over an entire Martian year (669 Earth days). MGS will now be deployed to study particularly interesting regions of Mars in more detail.

APOD: 2000 December 5 - Layered Mars: An Ancient Water World
Explanation: Pictured above, layers upon layers stretch across the floor of West Candor Chasma within the immense martian Valles Marineris. Covering an area 1.5 by 2.9 kilometers, the full image from the Mars Global Surveyor spacecraft shows over 100 individual beds. Each strikingly uniform layer is smooth, hard enough to form steep edges, and is 10 to 11 meters thick. In a press conference yesterday scientists Michael Malin and Ken Edgett presented this and other new images which show that the layered patterns exist at widespread locations near the martian equator. Their results indicate that some of the layered regions may be 3.5 billion years old. On planet Earth, layered patterns like these are formed from sediment deposited over time by large bodies of water. Likewise, the layered beds on Mars may be sedimentary rock formed in ancient lakes and seas. The researchers caution, however, that other uniquely martian processes may be responsible for the layering. Did life arise on ancient Mars? Because of their possible association with water, a prime location for future searches for fossil remains of martian life would be within these layers of Mars.

APOD: 2000 November 14 - The Yardangs Of Mars
Explanation: OK, fans of classic science fiction might be disappointed. The yardangs are not barsoomian warriors in a newly discovered Edgar Rice Burroughs tale of adventure and conquest on the Red Planet. In fact yardangs, geologists' term for narrow, wind-eroded ridges, are common land features in the desert regions of planet Earth. Such Eolian (wind related) landforms are common on Mars too, and this recently released Mars Global Surveyor picture shows long, sculpted yardangs in the eastern Aeolis region of southern Elysium Planitia. These martian yardangs may have formed in deposits of volcanic ash. Covering a swath of the martian surface 2.5 kilometers high, this composite image does offer special effects, though. If you have red/blue glasses (red for the left eye) you can view the yardangs of Mars in astounding 3-D!

APOD: 2000 September 12 - Slightly Above Mars Pathfinder
Explanation: If you could have hovered above the Pathfinder mission to Mars in 1997, this is what you might have seen. Directly below you is the control tower of Sagan Memorial Station. Three dark solar arrays extend out to collect valuable energy, surrounded by light-colored deflated airbags that protected Pathfinder's instruments from directly colliding with the rocky Martian surface. The left solar panel has ramps down which Pathfinder's rolling robot Sojourner started its adventure to nearby rocks. Sojourner itself is visible inspecting a rock nicknamed Yogi at 11 o'clock. Rocks cover the Martian surface, with Twin Peaks visible on the horizon at 9 0'clock. The distant sky is mostly orange. This image is a recently released digital combination of panoramic pictures taken by Pathfinder on Mars and a picture of a Lander scale model back on Earth. The Mars Pathfinder Mission was able to collect data for three months, sending back information that has indicated a wet distant past for Mars.

APOD: 2000 June 26 - Newton Crater: Evidence for Recent Water on Mars
Explanation: What could have formed these unusual channels? Inside a small crater that lies inside large Newton Crater on Mars, numerous narrow channels run from the top down to the crater floor. The above picture covers a region spanning about 3000 meters across. These and other gullies have been found on Mars in recent high-resolution pictures taken by the orbiting Mars Global Surveyor robot spacecraft. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists now hypothesize that liquid water did burst out here from underground Mars, eroded the gullies, and pooled at the bottom as it froze and evaporated. If so, life-sustaining ice and water might exist even today below the Martian surface -- water that could potentially support a human mission to Mars. Research into this exciting possibility is sure to continue!

APOD: 2000 June 23 - The Gullies Of Mars
Explanation: The recently revealed gullies on Mars are rare. But they may prove to be sites of present day, near surface, liquid water, holding out the tantalizing possibility of martian life. Too small to have been seen by past Mars orbiters, these disconcerting landforms were found in only about 250 out of more than 20,000 high resolution images from the operating Mars Global Surveyor spacecraft. Gullies found so far are located away from the martian equatorial region at middle and high latitudes (predominately in the south) and on poleward facing slopes. They are disconcerting because researchers have a compelling body of evidence that the martian gullies are related to groundwater seepage and, like their terrestrial counterparts, liquid water runoff -- on a planet whose surface is thought to be too cold and atmosphere too thin for liquid water to exist. The gullies in the three kilometer wide area pictured above are in the south facing wall of a crater in southern Noachis Terra. Unblemished by craters and overlaying young surface features, these and other gullies are inescapably young themselves. In fact, future monitoring of the martian gullies for changes could demonstrate whether the flows that formed them are still active today.

APOD: 2000 May 29 - Olympus Mons Volcano on Mars
Explanation: Scroll right to virtually climb the largest volcano in the Solar System. Olympus Mons on Mars measures three times higher than Earth's highest mountain, and has a volume over fifty times greater than Earth's largest volcano. The caldera at the top is over 70 kilometers wide. The low gravity and relatively static surface crust on Mars allows structures as large as Olympus Mons to form. Surrounding the volcano is a cliff that ranges up to 10 kilometers high. This black & white image is one of over 20,000 just-released images taken by the robot spacecraft Mars Global Surveyor that continues to orbit Mars.

APOD: 2000 May 14 - A Presidential Panorama of Mars
Explanation: Scroll right to unfold one of the great panoramas ever taken on the surface of Mars. For best viewing, click and hold the right arrow icon at the bottom of your browser window. This image, dubbed a "presidential panorama" by the Mars Pathfinder team, shows in colorful detail the surroundings of the Sagan Memorial Station. Now look closely at the big rock midway through the scrolling picture. That rock is called Yogi and just to its left is the robot Sojourner Rover taking measurements of it. Other now-famous rocks are also visible including Barnacle Bill and Flat Top. After this picture was taken Sojourner went on to analyze a rock named Scooby Doo. The Mars Pathfinder mission landed on 1997 July 4 and collected data for about three months. Analysis indicates that the Pathfinder site was likely awash in water in the distant past, but has been dry for the last two billion years.

APOD: 2000 March 23 - Inside Mars
Explanation: What's inside Mars? From orbit, the Mars Global Surveyor (MGS) spacecraft has recorded detailed images of the red planet since July 1997. Still, its cameras can not look beneath the surface. But minute changes in the spacecraft's orbital velocity are produced by variations in the planet's gravitational field, and these changes are related to interior density fluctuations. When the subtle orbital changes were measured using MGS radio science experiments and combined with the accurate Mars Orbiter Laser Altimeter topographical data, researchers were able to produce a map of the thickness of the martian crust. In this color cut-away diagram of the results, red colors correspond to thin and blue to thick areas of the crust which rides above the martian mantle. From the global map, the crust is seen to range from about 20 to 50 miles thick and shows a dramatic difference between the generally thinner northern hemisphere to thicker southern hemisphere crust. For the newly formed planet, the thin crust would have promoted rapid cooling and may have given rise to a large northern ocean on early Mars.

APOD: 2000 February 2 - Aeolian Mars
Explanation: Mars' atmosphere is relatively thin, still when martian winds blow they weather and shape its surface. Like familiar aeolian features on Earth, this field of dunes within Mars' Rabe crater exhibits graceful undulating ridges which can shift as windblown material is deposited on the dunes' windward face and falls away down the steeper leeward slopes. Indicated by the arrow, the dark trails are signs that the martian sand has avalanched down the steep slopes in the recent past. Rippling patterns of smaller dunes are also visible in this sharp high-resolution view along with criss-crossing dark trails which may be evidence of local dust-devil windstorms. The image is about 3 kilometers across and was recorded in March of 1999 by the orbiting Mars Global Surveyor spacecraft.

APOD: December 4, 1999 - Mars Polar Lander Target Ellipse
Explanation: South is up in this recent composite color picture of Mars Polar Lander's target region near the Martian South Pole taken on November 28. Imaged by the orbiting Mars Global Surveyor's wide angle camera, the area covered is 105 kilometers across with the expected landing ellipse superposed. It is late spring in Mars' southern hemisphere and white patches near the top are what remains of the area's winter frost while dark areas are likely sand and fields of sand dunes. The Mars Polar Lander spacecraft reached the Red Planet yesterday at 20:00 UTC and earthbound controllers are still trying to establish contact with the lander during the available communication windows. From orbit, the Mars Global Surveyor spacecraft will try to contact the two basketball-sized microprobes jettisoned during the lander's descent.

APOD: December 3, 1999 - Southern Mars
Explanation: This topographical map of the southern hemisphere of Mars was generated using data from the Mars Orbiter Laser Altimeter (MOLA). Flying on the Mars Global Surveyor spacecraft, MOLA has bounced a laser beam off the Martian surface over 200,000,000 times producing a wealth of detailed elevation measurements. The MOLA measurements have been color-coded so, for example, the white areas at left are the highest elevations in the southern Tharsis region and not snow-covered peaks. These areas are more than 6 kilometers above the hypothetical Martian "sea-level". Likewise, deep blues and purples are not water oceans but correspond to the lowest elevations (more than 4 kilometers below "sea-level"), like those found within the giant Hellas impact basin at right. In fact, liquid water is not present on Mars' surface today, but may have been in the past. NASA's Mars Polar Lander spacecraft is scheduled to embark on an investigation of the role of water in the climate history of the Red Planet. The lander is targeted to touch down within the long, thin ellipse indicated here just below the Martian South Pole today at 20:00 UTC.

APOD: October 30, 1999 - Mars Rocks, Sojourner Rolls
Explanation: This sharp color image featuring Mars rock Yogi and the rolling Sojourner robot shows off Yogi's two-toned surface. Yogi appears to be leaning into the prevailing winds causing some to suggest that its color contrast may be caused by the accumulation of rust colored dust on its windward face. The Pathfinder spacecraft, now the Sagan Memorial Station, has ended the primary mission phase after returning a scientific bonanza from the surface of Mars. The Sojourner robot rolled hundreds of feet on the martian surface, circumnavigated the lander, and produced a wealth of data and images. Mars Pathfinder and Soujourner landed on July 4, 1997 and lasted about 3 months, well beyond their designed lifetime.

APOD: August 16, 1999 - Mars Weather Watch
Explanation: Mars may be a cold, dry planet but its weather is dynamic. On June 30, wide angle cameras on board the Mars Global Surveyor (MGS) spacecraft watched the development of this large scale storm system above Mars' north polar area. These frames were recorded on successive mapping orbits at intervals of about 2 hours, with the white north polar cap near the center of each. High winds seem to mix the brownish dust clouds and white water-ice clouds as the curling storm front churns over the extreme northern martain landscape. The MGS cameras have watched similar storms in this region during the months of July and August revealing surprisingly complex weather. Mars Climate Orbiter will join the MGS spacecraft in martian orbit in late September, and in December Mars Polar Lander is scheduled to touch down near the Red Planet's south pole.

APOD: July 5, 1999 - Four Faces of Mars
Explanation: As Mars rotates, most of its surface becomes visible. During Earth's recent pass between Mars and the Sun, the Hubble Space Telescope was able to capture the most detailed time-lapse pictures ever from the Earth. Dark and light sand and gravel create an unusual blotted appearance for the red planet. Winds cause sand-tinted features on the Martian surface to shift over time. Visible in the above pictures are the north polar cap, made of water ice and dry ice, clouds including an unusual cyclone, and huge volcanoes leftover from ancient times. The Mars Global Surveyor satellite orbiting Mars continues to scan the surface for good places to land future robot explorers.

APOD: July 4, 1999 - A Landing On Mars
Explanation: On July 4th, 1997 - using its own array of fireworks, a parachute, and airbags - the Mars Pathfinder spacecraft successfully came to rest on the surface of Mars at 10:07 AM Pacific Daylight Time. Ninety minutes before reaching the surface Pathfinder began a flurry of activity. The robot spacecraft vented cooling fluid, jettisoned its cruise stage, decelerated at 20 gees on atmospheric entry, deployed a 24 foot parachute, jettisoned its heat shield, slid down a 60 foot bridle, fired solid fuel braking rockets, deployed a cocoon of airbags, separated from the bridle, impacted the martian surface, bounced a few times (traveling about 300 - 600 feet between bounces), settled on the surface, deflated the airbags, and righted itself, all under the autonomous control of the onboard computer. Above is a mosaic of images transmitted shortly after Pathfinder reestablished communication with its operators on Earth. The solar powered, two foot long, 25 pound Mars Sojourner robot rover is visible crouched on the unfolded spacecraft. Beyond lie deflated airbags, rock-strewn terrain, distant hills, and a dusty brown martian sky.

APOD: June 2, 1999 - Thermal Mars
Explanation: It's 2 AM on Mars and surface temperatures range from -65C to -120C, as measured by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor spacecraft. TES data used to make this detailed temperature map were acquired while passing over the night side of the Red Planet during 500 mapping orbits of Mars. With the warmest temperatures shown in white, progressing through red, yellow, and green colors to the coldest temperatures in blue, the map reveals the northern hemisphere during summer while the south experiences the cold martian winter. Near Mars' equator, the variations in nighttime temperatures are related to surface materials. Cold blue areas are covered with fine dust particles and the warmer regions are covered with coarser sand and rocks.

APOD: May 28, 1999 - Topographical Mars
Explanation: Contrasting colors trace changing elevations in this new high-resolution topographic map of Mars. Just released, the data were gathered in 1998 and 1999 by the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor spacecraft. The martian topography is seen to range over 19 miles between the highest volcanic peaks (white) and the lowest regions (purple). Along with the striking difference between the Red Planet's low northern hemisphere (top) and high southern regions, one of the most noticeable features on the map is the large blue-purple southern depression corresponding to the Hellas basin. Likely the result of an asteroid impact, Mars' deepest basin is about 1300 miles across making it one of the largest impact features in the Solar System. Explorations of MOLA's rich topographic database are expected to produce insights into water flows and the geologic history of Mars.

APOD: May 20, 1999 - Cyclone on Mars
Explanation: Late last month a team of Mars-watching astronomers sighted an immense cyclonic storm system raging near the Red Planet's north pole. Their discovery picture, made with the Hubble Space Telescope on April 27, is seen at left while the projected insets (right) show closeups of the storm and surrounding areas. Shrunken to its martian midsummer state, Mars' north polar cap appears at the top of the discovery picture. The polar cap is clearly smaller than the storm just below it and farther left. Similar to the "spiral storms" detected on Mars over 20 years ago by the Viking spacecraft, this storm was marked by a system of swirling bright water-ice clouds instead of the billowing dust of a more typical martian wind storm. Measuring roughly 1,000 miles across, with a cloud-free central eye spanning about 200 miles, it was comparable in size to cyclones seen in planet Earth's polar regions. The storm system was imaged once more, hours later, but then was not seen again and may have had a lifetime of only a few days.

APOD: May 13, 1999 - Mars Volcano Apollinaris Patera
Explanation: Dwarfed by Olympus Mons and the other immense shield volcanos on Mars, Apollinaris Patera rises only 3 miles or so into the thin martian atmosphere, but bright water-ice clouds can be still be seen hovering around its summit. Mars' volcanic structures known as "paterae" are not only smaller than its shield volcanos but older as well, with ages estimated to be around 3 billion years. Like Apollinaris Patera, narrow furrows typically extend from their central craters or calderas. It is thought that the paterae represent broad piles of easily eroded volcanic ash. This wide angle view of Apollinaris Patera was recorded last month by the Mars Global Surveyor spacecraft. The large central crater is about 50 miles across.

APOD: May 4, 1999 - Magnetic Mars
Explanation: Mapping Mars from orbit, instruments on the Mars Global Surveyor (MGS) spacecraft have recently revealed banded magnetic field patterns - a startling and unanticipated suggestion that the Red Planet was more Earth-like in its distant past. The red and blue regions within the MGS orbital tracks across this portion of southern Mars indicate adjacent areas of crust where magnetic fields point in opposite directions. The bands seem to run east-west and are about 100 miles wide and 600 miles long. Such patterns are known to be produced on Earth by plate tectonics. As the crustal plates spread apart along the mid-ocean ridges, they carry a progressive banded record of Earth's changing magnetic field. The similar patterns on Mars are seen as evidence that it too once had moving crustal plates and a changing magnetic field, although both processes - still active on the larger planet Earth - are thought to have long since died away. These high resolution measurements of martian magnetism were made possible by the revised, close aerobraking orbits of the MGS spacecraft and not originally planned.

APOD: April 28, 1999 - A Sundial for Mars
Explanation: When Mars Surveyor arrives at Mars in 2002, it will carry a sundial. Even though batteries and a solar array will power the Mars Surveyor Lander, the sundial has been included to allow a prominent public display of time. The sundial idea was the brainchild of Bill Nye the Science Guy, who noticed that a post originally used for camera calibration could be redesigned. Millennia ago, sundials were state-of-the-art timekeepers for humans on Earth. Since the Sun casts similar shadows on Mars and Earth, accurate calibration of the shadow placement on the Martian Sundial will tell a curious inspector of returned images both the time of day and the season.

APOD: April 1, 1999 - Ski Mars
Explanation: These brightly reflecting fields of snow or frost are on the slopes of a crater rim in the northern hemisphere of Mars. They are 500 meters or so long and have lasted through about eight months of the Red Planet's spring and summer weather. Recently imaged by the Mars Global Surveyor spacecraft, they also seem to be relatively uncrowded ... suggesting to some on April 1st, that lift tickets on Mars are extremely expensive. Of course, a vacation on the Red Planet could still offer some advantages to skiing and snowboarding enthusiasts. For example, Mars' low gravity - only about 3/8ths Earth's gravity - would definitely tend to reduce sore muscles and fall-related injuries. Happy April Fools day from APOD.

APOD: March 19, 1999 - Mapping Mars
Explanation: This month, the Mars Global Surveyor (MGS) spacecraft began its primary mission to the red planet. Orbiting about once every two hours at an altitude of over 200 miles, instruments onboard MGS now regularly explore the Martian surface and atmosphere. This MGS polar mapping orbit was set up to achieve a favorable "afternoon" sun-angle for imaging as the spacecraft crosses over the day side of the planet. Mars' rotation will allow complete coverage of the surface roughly once every week with mapping operations planned for one Martian year (687 Earth days). These two opposite hemisphere views of Mars were pieced together from MGS wide-angle camera scans made in early March (blue and red lines mark the scan edges). Water-ice clouds can be seen hovering over the surface while the north polar cap is visible at the top of each image.

APOD: March 15, 1999 - Happy Face Crater on Mars
Explanation: Even Mars can put on a happy face. The Martian crater Galle has internal markings reminiscent of a smiley face symbol. Such markings were originally discovered in the late 1970s in pictures taken by the Viking Orbiter. A large meteor impacted the Martian surface to form the crater. Conventional wisdom holds that the markings inside the crater are placed by chance by natural processes. The Mars Global Surveyor (MGS) spacecraft currently orbiting Mars took the above picture. MGS recently started the global surveying phase of its mission.

APOD: March 3, 1999 - Infrared Mars
Explanation: Was Mars wetter and more Earth-like in its distant past? This false-color composite image of Mars is part of the mounting evidence that liquid water once did play a significant role in Martian surface geology. Constructed from infrared imaging data obtained by the Hubble Space Telescope in July 1997, the north polar cap is near the top of the picture and the large reddish region indicates potential water-bearing mineral deposits. Mars Pathfinder landed at the southern edge of this area, known as the Mare Acidalium, also finding evidence of water-worn conglomerate rocks. Large scale surface features in this region appear to have been sculpted by massive flooding in the early history of Mars.

APOD: December 24, 1998 - Mars Climate Orbiter Launches
Explanation: Looking down from atop a Delta II rocket blasting skyward, solid fuel boosters fall away (left) and the Earth's limb slides into view. These pictures from the launch of the Mars Climate Orbiter were taken as it climbed away from Cape Canaveral Air Station Space Launch Complex 17 on December 11. This spacecraft won't arrive at Mars in time for Christmas though, as its cruise to the red planet will require about 9 1/2 Earth months to complete. Once it does get there it will use aerobraking to help establish a polar science mapping orbit for studying the martian atmosphere. The orbiter is also scheduled to act as a communications relay for the soon to be launched Mars Polar Lander.

APOD: December 16, 1998 - 3-D Mars North Pole
Explanation: This dramatic premier three-dimensional visualization of Mars' north pole is based on elevation measurements made by an orbiting laser. During the Spring and Summer of 1998 the Mars Orbiter Laser Altimeter (MOLA) flashed laser pulses toward the Martian surface from the Global Surveyor spacecraft and recorded the time it took to detect the reflection. This timing data has now been translated to a detailed topographic map of Mars' north polar terrain. The map indicates that the ice cap is is about 1,200 kilometers across, a maximum of 3 kilometers thick, and cut by canyons and troughs up to 1 kilometer deep. The measurements also indicate that the cap is composed primarily of water ice with a total volume of only about four percent of planet Earth's Antarctic ice sheet. In all it represents at most a tenth of the amount of water some scientists believe once existed on ancient Mars. Where did all the water go?

APOD: September 24, 1998 - The North Pole Of Mars
Explanation: The North Pole of Mars is capped by layers likely consisting of ice and dust deposited over millions of years. Imaged on September 12 - early Spring for Northern Mars - by the Mars Global Surveyor's camera, this synthesized wide-angle color view shows the rippled, eroded polar terrain covered with pinkish seasonal carbon dioxide frost. Dark areas bordering the polar cap are fields of sand dunes. This is the last picture scheduled to be taken by Surveyor's camera until it resumes operation in late March 1999. Over the past year of operation, the camera has taken about 2,000 pictures of Mars. Meanwhile, the spacecraft will begin its second round of aerobraking to achieve a circularized martian mapping orbit.

APOD: August 14, 1998 - The Dunes Of Mars
Explanation: The North Pole of Mars is ringed by a "sea of sand dunes". For Mars' Northern Hemisphere, Spring began in mid July and increased sunlight is now shrinking the polar cap revealing the wind-swept dunes to the cameras onboard the Mars Global Surveyor spacecraft. North is up in this recently released close-up which covers a region about 1.2 miles across at 77 degrees Northern Martian Latitude. These dunes have been formed by winds generally blowing from the Southwest and are still covered with scattered white patches of carbon dioxide frost. Near the end of January 1999 Summer will begin and offer even clearer views of Northern dunes of Mars.

APOD: July 30, 1998 - Volcanos on Mars: Elysium Region
Explanation: This "synthetic color" image swath of the Elysium Volcanic Region of Mars was recorded by Mars Global Surveyor's wide angle camera on July 2. North is up and the sun illuminates the scene from the lower right. Bright clouds hover near the northern most dome-shaped volcano Hecates Tholus. The shield volcano Elysium Mons lies about 250 miles south near the image center, and farther south lies another dome-shaped volcano, Albor Tholus, with a broad summit basin or caldera. Even though Mars is just half the size of planet Earth, it is known for its volcanos - the largest of which dwarf their terrestrial counterparts.

APOD: June 19, 1998 - Good Morning Mars
Explanation: Looking down on the Northern Hemisphere of Mars on June 1, the Mars Global Surveyor spacecraft's wide angle camera recorded this morning image of the red planet. Mars Global Surveyor's orbit is now oriented to view the planet's surface during the morning hours and the night/day shadow boundary or terminator arcs across the left side of the picture. Two large volcanos, Olympus Mons (left of center) and Ascraeus Mons (lower right) peer upward through seasonal haze and water-ice clouds of the Northern Martian Winter. The color image was synthesized from red and blue band pictures and only approximates a "true color" picture of Mars.

APOD: June 8, 1998 - A Mars Glint
Explanation: If aligned just right, even a planet can produce a glint. The above combined pictures of Mars make the red planet appear unusually elongated - Mars is really almost spherical. However, these pictures were taken when the Sun was nearly directly behind the Mars Global Surveyor (MGS) spacecraft. This created a view for MGS where every part of Mars that was visible was also illuminated by the Sun. From this vantage point, though, sunlight reflects off the Martian surface and atmosphere producing a bright spot in the center - a glint. The brightness, color, and extent of the glint carry valuable information about the composition and physical properties of Mars.

APOD: May 31, 1998 - Phobos: Doomed Moon of Mars
Explanation: Phobos is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These Martian moons may well be captured asteroids originating in the asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1977 Viking orbiter image, the largest moon, Phobos, is seen to be a heavily cratered asteroid-like object. It is about 17 miles across and zips through the Martian sky completing an orbit in less than 8 hours. Phobos orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it should crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: April 30, 1998 - Mars: Big Crater in Stereo
Explanation: Get out your red/blue glasses and check out this stereo picture of "Big Crater" on Mars! (Pieces of red and blue or green clear plastic will do. Your right eye should look through the red piece.) The stereo perspective was created by combining images from the Mars Global Surveyor spacecraft taken on two different orbits, each with a slightly different viewing angle. At just under a mile in diameter, Big Crater is not all that big but it is an important landmark in the vicinity of the Mars Pathfinder landing site on an ancient flood plain in Ares Vallis. Identifying corresponding smaller scale features in Pathfinder and Surveyor images will help to precisely locate the lander. Meanwhile, the line of sight between the Earth and Mars is approaching the Sun. During this period, known as solar conjunction, communicating with Mars Global Surveyor will be difficult.

APOD: April 17, 1998 - Mars: Looking For Viking
Explanation: On July 20, 1976, the Viking 1 lander touched down on the Martian Chryse Planitia. Its exact landing site is somewhere in the white rectangle above. Unfortunately, this wide angle Mars Global Surveyor image taken on April 12 reveals a substantial dust storm in the area with light colored plumes apparently blowing toward the upper right of the picture. Attempts to find the first spacecraft to land on Mars in the corresponding high resolution narrow field images have not been successful due in part to the increased atmospheric haze. The region shown here is about 100 miles across.

APOD: April 16, 1998 - Mars: Cydonia Close Up
Explanation: The Mars Global Surveyor spacecraft has returned another close-up of the Cydonia region on Mars. Orbiting over clear Martian skies at a range of about 200 miles, the Mars Orbiter Camera looked down on features known as the "City" on Mars and produced a high resolution image covering a swath around 1.5 by 15 miles at a pixel size of about 8.2 feet. This cropped portion of the processed image shows an area approximately 1.5 miles wide. Heavily weathered hills and pocked surfaces suggest the erosion of layers of the ancient Martian crust.

APOD: April 6, 1998 - A Face On Mars
Explanation: This image, showing what looks to be a human face (above center) and other features of the Cydonia region on the Martian surface, was produced using data from NASA's Viking 1 orbiter in 1976. Described in a NASA press release as a "rock formation which resembles a human head", some have since offered the extraordinary explanation that the face is an artificial construct built by a civilization on Mars! However, most scientists have a more conventional view - that this feature is indeed a natural Martian hill whose illusory face-like appearance depends on illumination and viewing angle. This month, the Mars Global Surveyor satellite will be in position to take new pictures of this region of controversial Martian features along with areas around the Mars Pathfinder and Viking landing sites.

APOD: March 20, 1998 - Mars: Ridges Near the South Pole
Explanation: No, it's not breakfast ... but looking down from an orbiting spacecraft, the odd intersecting ridges covering this area of Mars do present a waffle-like appearance. The cause of the ridge pattern is unknown but it suggests that more complex layered deposits lie below. The south polar region in this Mars Global Surveyor image measures about 8.5 by 12 miles and is spread with a layer of bright, seasonal carbon dioxide frost. Mysterious dark spots which pepper some of the interridge areas are 60 to 300 feet across. Their exact nature is also unknown, but these spots have apparently defrosted early and lack the bright layer of frozen carbon dioxide.

APOD: March 17, 1998 - Clouds Over Tharsis on Mars
Explanation: When and where do clouds form on Mars? The Mars Global Surveyor spacecraft currently orbiting Mars is finding out. Photographs released last week showed clouds forming above Tharsis, a huge bulge on Mars about 4000 kilometers across and 7 kilometers high containing several large volcanoes. These clouds temporarily disappeared as a large dust storm emerged from the South, the first developing dust storm to be tracked by an orbiting spacecraft. Mars Global Surveyor continues to aerobrake during on its ongoing mission to survey the planet Mars.

APOD: March 9, 1998 - Yogi Rock on Mars
Explanation: Yogi is possibly the best photographed rock on Mars. By combining many pictures taken during the Mars Pathfinder Mission last year, scientists were able to create a super-resolution, digitally enhanced image that better allows them to study Yogi's surface and more accurately determine how Yogi was formed. The smoothness of some Martian rocks suggests previous interactions with water, implying that Mars was both warmer and wetter in the past.

APOD: February 12, 1998 - In A Grand Canyon On Mars
Explanation: In a grand canyon on Mars, steep slopes fall away from a smooth plateau revealing striking layered rock formations. The canyon is part of the Valles Marineris, a 2,500 mile long system of canyons cutting across the Martian equator. This view, recorded on January 1 by the orbiting Mars Global Surveyor shows a small portion of Valles Marineris in amazing detail. The image is about 6 miles wide and high resolution versions show features as small as 20 feet across. What processes caused the layering? In the Grand Canyon on planet Earth, sedimentary processes have resulted in spectacular rock layers. But similar layers of rock in canyons of the Hawaiian Islands were created by volcanoes. Regardless of the origin of layering on Mars, its extent suggests that early Mars was geologically active and complex.

APOD: February 10, 1998 - All of Mars
Explanation: Mars Global Surveyor is photographing Mars. The robot spacecraft arrived last September and continues to use solar panel aerobraking to help maneuver it to a better orbit to survey all of Mars The above image is a reconstruction of several photographs digitally combined to simulate a single vantage point 2700 kilometers above the Martian surface. The images were taken by the Mars Orbital Camera in wide angle mode in late December 1997. Visible features include the Valles Marineris canyon across the top, and the South Polar Cap of frozen carbon dioxide at the bottom. Many finer features that would normally be visible are hidden by dust remaining from a planet-wide storm that subsided only three weeks before these images were recorded.

APOD: November 13, 1997 - Mars: A Sheer Close Up
Explanation: As the Mars Global Surveyor spacecraft maneuvers toward its final mapping orbit, its cameras have been producing some sharp views of Mars. At a resolution of better than 30 feet per pixel, this image of a portion of the immense canyon, Valles Marineris, highlights the sheer mountain cliffs over 3200 feet tall near the canyon walls. The striking and extensive layering clearly apparent in the triangular mountain face was totally unanticipated. This exciting new result challenges common theories about the surface of Mars and argues that a complex early geological history is responsible for the current Martian landscape.

APOD: October 31, 1997 - Haunting Mars
Explanation: This Halloween, the news about Mars is good news - Mars Global Surveyor will resume aerobraking into a mapping orbit around the haunting red planet. Wide angle cameras onboard the spacecraft recently recorded this shadowy image of Olympus Mons, the Solar System's largest volcano, from an altitude of over 100 miles. The summit depression or caldera of Olympus Mons is about 40 miles across and 15 miles above the Martian surface. On Halloween Night in 1938, Mars also made the news when Orson Welles' radio theatre adaptation of H.G. Wells' "War of the Worlds" - a fictional account of invaders from Mars - was dramatized as a live news report. The performance was so convincing it tricked some listeners, but most who heard the broadcast felt it was a treat. Have a happy and safe Halloween!

APOD: October 13, 1997 - Ice Clouds over Mars
Explanation: Mars has clouds too. The above true color image taken in August by Mars Pathfinder shows clouds of ice high in the Martian atmosphere. Unlike Earth's atmosphere which is composed predominantly of nitrogen and oxygen, Mars' atmosphere is composed mostly of carbon dioxide. Nevertheless, a trace amount of water does freeze into visible clouds at night, which become particularly apparent during the day by reflection of sunlight. Contact was lost with Mars Pathfinder last Sunday but re-established later in the week.

APOD: October 6, 1997 - Surveyor At Mars
Explanation: Mars Global Surveyor achieved Martian orbit on September 11 and began aerobraking into its final mapping orbit, a process that will take until March next year. Anticipating the labors ahead, Mars Orbital Camera operators have begun acquiring test images. This dramatic detail of a recent image shows a 10 mile wide swath of a highland valley, part of the Nirgal Vallis system. The original image was recorded from an altitude of 250 miles at a resolution of about 30 feet per pixel and has been rotated to represent the camera's perspective view. Were these valleys formed by flowing water or did collapse and erosion caused by ground water produced the channel? What other processes were important? Time will tell. From its planned mapping orbit, with four times better resolution, Mars Global Surveyor's images should provide answers to these and other questions about Mars.

APOD: September 15, 1997 - Olympus Mons on Mars: The Largest Volcano
Explanation: The largest volcano in the Solar System is on Mars. Olympus Mons rises 24 kilometers high and measures 550 km across. By comparison, Earth's largest volcano, Mauna Loa in Hawaii, rises 9 km high and measures 120 km across. Such large volcanoes can exist on Mars because of the low gravity and lack of surface tectonic motion. Olympus Mons is a shield volcano, built by fluid lava. Over the next three years, Mars Global Surveyor, which arrived at Mars last week, will photograph the planet at such high resolution that objects only 100 meters across will be visible. The above image was taken by Mariner 9, which orbited and photographed Mars during 1971 and 1972.

APOD: September 11, 1997 - Mars Global Surveyor: Aerobraking
Explanation: Completing a 10 month journey, another spacecraft from Earth arrives at Mars today. The Mars Global Surveyor (MGS) is scheduled to fire its main rocket engine for 22 minutes at 6:17 p.m. PDT and enter a highly elliptical orbit, with a low point 186 miles and a high point 34,800 miles above the surface of Mars. This robot spacecraft is aptly named. Its mission is to undertake a detailed planetwide survey of Mars. But first MGS must circularize its orbit, lowering the high point to about 250 miles. Instead of relying solely on its rocket engine, MGS mission controllers will use a fuel-saving technique known as aerobraking - dipping the spacecraft into the Martian atmosphere where it will encounter increased atmospheric drag. This early artist's conception emphasizes the drag created by the wing-like solar panels. The cumulative effect should find MGS in a more circular mapping orbit by March 1998. To successfully use aerobraking, mission controllers must achieve an exact orbit and will be handicapped by a limited knowledge of the thickness of the Martian atmosphere. They may even need to alter the spacecraft's course to compensate for changes in Martian weather.

APOD: August 4, 1997 - A Rusty Sunset on Mars
Explanation: On Mars, sunsets can appear salmon pink. The unusual color is partly due to rust: oxidized iron from Martian dust circulating in the Martian atmosphere. Clouds appear in the morning and evening, but usually evaporate in the midday Sun. A day on Mars lasts 24.6 hours - very similar to Earth's, but a Martian year lasts almost twice as long as an Earth year. The above panorama by Mars Pathfinder, shown mirror-inverted, was released last Friday by the Imager team. Mars Pathfinder has now successfully completed all the goals of its planned mission. Nevertheless, the Sagan Memorial Station spent the weekend recharging its batteries, anticipating the possibility of still more productive weeks of exploration ahead.

APOD: July 16, 1997 - Mars: Yogi And Friends in 3D
Explanation: A ramp from the Pathfinder lander, the Sojourner robot rover, airbags, a couch, Barnacle Bill, and Yogi Rock appear together in this 3D stereo view of the surface of Mars. Barnacle Bill is the rock just left of the solar-paneled Sojourner and Yogi is the big friendly-looking boulder at the right. The "couch" is the angular rock shape visible on the horizon. Look at the image with red/blue glasses (... or just hold a piece of clear red plastic over your left eye and blue or green over your right) to get the dramatic 3D perspective. The stereo view was recorded by the remarkable Imager for Mars Pathfinder (IMP) camera. The IMP has two optical paths for stereo imaging and ranging and is equipped with an array of color filters for spectral analysis. Operating as the "first astronomical observatory on Mars" the IMP has also recorded images of the Sun and Deimos, the smallest of Mars' two tiny moons. Overcoming communications problems and computer resets the Pathfinder is transmitting new color images which should be available July 18.

APOD: July 5, 1997 - Pathfinder on Mars
Explanation: Yesterday, July 4th, using its own array of fireworks, a parachute, and a cocoon of airbags, the Mars Pathfinder spacecraft successfully bounced and came to rest on the surface of Mars at 10:07 AM Pacific Daylight Time. And the news is wonderful - the spacecraft appears to be in good health after having performed its complicated landing sequence superbly. Above is a mosaic of images from the martian surface transmitted shortly after Pathfinder reestablished communication with its mission operators on Earth. The solar powered, two foot long, 25 pound Mars Sojourner robot rover is visible crouched on the unfolded spacecraft. Surrounding Pathfinder are deflated airbags and a rock-strewn terrain. In the distance martian hills appear against a dusty brownish sky. The IMP camera which produced this view is also capable of stereo images and promises further spectacular pictures from Mars.

APOD: June 27, 1997 - Mars: Just The Facts
Explanation: Mars, the freeze-dried planet, orbits 137 million miles from the Sun or at about 1.5 times the Earth-Sun distance. It has two diminutive moons, towering extinct volcanos, an immense canyon system, a thin atmosphere chiefly composed of carbon dioxide (CO2), a frigid average surface temperature of -63 degrees Celsius, and permanent frozen CO2 polar caps which contain some water ice. Mars' surface presently lacks liquid water and has a reddish color because of an abundance of oxidized iron compounds (rust). A small terrestrial planet, fourth from the Sun, Mars has only about 3/8 the surface gravity of Earth. So for example, if you tip the scale at a hefty 200 pounds on Earth you'd be a 75 pound featherweight on Mars. The low martian gravity will be good for NASA's Mars Pathfinder spacecraft scheduled to land on Mars next Friday, July 4th. Using rockets, parachutes, and airbags, Mars Pathfinder will be the first spacecraft to touchdown on the planet since the Viking landers in 1976. Pathfinder is also scheduled to begin the first ever mobile surface exploration by releasing the robot rover, "Mars Sojourner".

APOD: May 28, 1997 - Mars: Just The Fiction
Explanation: For centuries, astronomers have observed Mars, patiently compiling many facts and theories. Like a distant mirror of Earth dwellers' hopes and fears for the future, Mars, the fourth planet from the sun, has inspired profound works of fiction as well. Classics of the science fiction genre with visions of Earth's alluring planetary neighbor include H.G. Wells' terrifying "War of the Worlds", Edgar Rice Buroughs' John Carter adventure series (Thuvia, Maid of Mars, The Gods of Mars, A Princess of Mars, The Warlord of Mars), Robert Heinlein's youthful "Podkayne of Mars", and Ray Bradbury's reflective and philosophical "The Martian Chronicles". Through the years scientific theories about Mars have been disproven, but the sense of wonder and adventure embodied in these works of fiction remain with us. As two spacecraft from Earth now draw close to the red planet- in dreams, desires, and a quest for knowledge - we are once again bound for Mars.

APOD: March 24, 1997 - The Weather on Mars
Explanation: Would Mars be a nice place to visit? Sometimes. Much of Mars undergoes severe changes in climate during its orbit around the Sun, ranging from extreme cold to temperatures enjoyable by humans. But Mars is usually a nice place to visit for hardy spacecraft, and in fact the Mars Pathfinder and Mars Global Surveyor missions are currently headed for the "Red Planet." In preparation for the scheduled Mars Pathfinder landing on July 4^th, 1997, the Earth-Orbiting Hubble Space Telescope recently took the above high resolution photograph. The picture shows the onset of Martian summer (northern hemisphere) when, apparently, the northern polar cap recedes to uncover dark sand dunes.

APOD: August 7, 1996 - Early Microscopic Life on Mars?
Explanation: Today a team of NASA and Stanford scientists announced the discovery of strong circumstantial evidence that microscopic life once existed on Mars. Dr. David McKay, Dr. Everett Gibson, and Kathie Thomas-Keprta of Lockheed-Martin, all from (NASA /JSC), and Dr. Richard Zare (Stanford) have led a team that has found chemical evidence for past life on Mars - including what they interpret as possible microscopic fossil remains (tube-like structures pictured above) - in a meteorite thought to have originated on Mars. A small fraction of the many meteorites that fall to Earth from space have composition similar to the Martian surface. Many scientists believe that these meteorites are indeed Martian rocks that have been catapulted into space during a catastrophic event on Mars, such as an asteroid impact. The escaped rocks would then circle the inner Solar System, some of them falling to Earth. The meteorite containing the evidence landed on Earth 13,000 years ago, but may indicate a life-form that existed on Mars billions of years ago. The team's findings will be published in the August 16 issue of Science Magazine. Even skeptical scientists look forward to future research confirming or refuting these exciting claims.

APOD: July 20, 1996 - 20 Years Ago: Vikings on Mars
Explanation: On July 20, 1976, NASA's Viking 1 lander become the first spacecraft to land on Mars, followed weeks later by its twin robot explorer, the Viking 2 lander. Operating on the Martian surface into the early 1980s, the Vikings took thousands of pictures, conducted sophisticated chemical searches for life and studied the Martian weather and geology. In the dramatically detailed image above, a field of rocks and boulders is viewed from the Viking 1 landing sight on Chryse Planitia (the Plain of Chryse). Viking 1's dusty foot pad is just visible at the lower right. The image was created by combining high resolution black and white images with lower resolution color images of the same area. NASA is planning to continue its extremely productive and well chronicled exploration of the mysterious Red Planet with the Mars Global Surveyor and the Mars Pathfinder missions. What's Mars like today?

APOD: October 2, 1995 - Phobos: Doomed Moon of Mars
Explanation: Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These Martian moons may well be captured asteroids originating in the asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1977 Viking orbiter image, the largest moon, Phobos, is seen to be a heavily cratered asteroid-like object. It is about 17 miles across and zips through the Martian sky completing an orbit in less than 8 hours. Phobos is doomed. It orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it could crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: July 22, 1995 - The Face on Mars
Explanation: This image, showing what looks to be a human face sculpted on the martian surface, was produced using data from NASA's Viking 1 orbiter in 1976. Described in a press release as a "face-like hill" it caused some to offer the sensational speculation that it was an artificial construct built by an intelligent civilization on Mars! As a result, this image was splashed across the covers of many grocery store tabloids at the time. A detailed analysis of multiple images of this feature reveals a natural looking martian hill whose illusory face-like appearance depends on viewing angle and angle of illumination.

APOD: July 21, 1995 - The Search for Life on Mars
Explanation: Although images of Mars taken from space revealed the planet to have a barren and cratered surface, scientists did not give up the search for martian life. In 1976 NASA's Viking project succeeded in landing two robot probes on the surface of Mars. These landers were able to carry out sophisticated chemical experiments to look for signs of microscopic life in the martian soil. However, the experiments failed to produce any convincing evidence for life on Mars. Cameras onboard the Viking Landers also returned spectacular photos of the rocky martian landscape, like the one above, which showed no sign of martian animal or plant life.

APOD: July 20, 1995 - The Grand Canyon of Mars
Explanation: The Mariner Valley, also known as the Valles Marineris canyon system, appears in this mosaic of images from NASA's Viking spacecraft as a huge gouge across the red planet. This "Grand Canyon" of Mars is about 2500 miles long and up to 4 miles deep. By comparison, the Earth's Grand Canyon is less than 500 miles long and 1 mile deep.

APOD: July 19, 1995 - The Mountains of Mars
Explanation: Volcanic activity on Mars has produced towering mountains. The largest one, Olympus Mons, is pictured here in this Viking Orbiter image. Olympus Mons is a shield volcano nearly 15 miles high and over 300 miles wide at its base. By comparison, Earth's largest volcano, Mauna Loa in Hawaii, is just over 5 miles high and about 12 miles wide.

APOD: July 16, 1995 - The Exploration of Mars
Explanation: Thirty years ago NASA's exploration of Mars began. In July of 1965 the Mariner 4 spacecraft flew within 6,000 miles of Mars and returned 21 pictures of the mysterious red planet. NASA's continued exploration of Mars has produced detailed views of the red tinged Martian surface like the one shown above which is a composite of 102 images from the Viking missions to Mars . The composite was constructed by the US Geological Survey.