The Perfect Dust Storm Strikes Mars

Three months after it began, an awesome global dust storm on Mars is waning. Two NASA spacecraft have captured dazzling images of the planetary tempest.

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October 11, 2001: A pair of NASA spacecraft, the Mars Global Surveyor (MGS) and Hubble Space Telescope, is giving scientists a ringside seat for the biggest global dust storm seen on Mars in several decades. The extraordinary storm, which first enveloped the Red Planet three months ago, is finally subsiding -- but researchers say it could flare up again at any time.

Above: These Hubble Space Telescope images show the Red Planet before (left) and during (right) the great Martian dust storm of 2001. [more information]

"This is an opportunity of a lifetime," says Hubble observer James Bell of Cornell University. "We have a phenomenal, unprecedented view from these two spacecraft."

"The beauty of Mars Global Surveyor is that we have almost two Martian years of continuous coverage and this is the first time during the mission that we have seen such a storm," added Richard Zurek of NASA's Jet Propulsion Laboratory.

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Earth has dust storms, too, but the planet-girdling storms on Mars dwarf their terrestrial counterparts. (See Science@NASA's "Planet Gobbling Dust Storms" for more information.) No one knows exactly how Martian dust storms grow to such awesome proportions. But researchers hope the ongoing event -- observed so thoroughly by Hubble and MGS -- might provide some answers.

Martian dust storms not only cloud the Red Planet's air, they also warm its atmosphere. The temperature of Mars' upper atmosphere soared 80 degrees Fahrenheit during the storm -- a result of sunlight heating airborne dust grains. In a curious twist, the onset of global warming in the thin atmosphere marked the beginning of a cool period on the planet's surface, which has chilled under the near-constant shroud of dust.

The warmer atmosphere "puffed up" during the storm -- a condition that affects Mars-orbiting spacecraft by increasing the amount of aerodynamic drag at orbital altitudes. As a result, the storm is being closely monitored by the team operating NASA's 2001 Mars Odyssey spacecraft, due to arrive at Mars later this month. That spacecraft will circularize its orbit around Mars by means of aerobraking. The Odyssey team plans to "toe-dip" its way into the Martian atmosphere, gradually deepening its pass through the atmosphere until the desired drag levels are found.

Below: MGS infrared measurements reveal how the Martian atmosphere has substantially warmed during the ongoing dust storm. GIF animations: Large (1 MB, includes an extended caption), Medium (450 kb), or Small (70 kb). Credit: the ASU Thermal Emission Spectrometer Team.

The Thermal Emission Spectrometer (or "TES") -- an infrared instrument on MGS -- has been tracking the dust storm from Mars orbit by measuring temperature changes that trace the amount and location of dust in the atmosphere. Meanwhile, the spacecraft's Mars Orbiter Camera (MOC) has captured detailed pictures of the Martian surface in visible light. Such close-up monitoring has allowed scientists to pinpoint places where dust was being raised, and to see it migrate and interact with other Martian weather phenomena and surface topography. It has also provided an unprecedented detailed look at how storms start and "blossom" across the orange arid planet.

The Hubble Space Telescope doesn't offer continuous Mars coverage, as MGS instruments do, but it does reveal the whole planet in a single snapshot and shows the full range of dust activity from sunrise to sunset. Together, Hubble and MGS provide a complete picture.

"What we have learned is that this is not a single, continuing storm, but rather a planet-wide series of events that were triggered in and around the Hellas basin," says Mike Malin of Malin Space Science Systems, Inc., lead investigator for the MOC. "What began as a local event stimulated separate storms many thousands of kilometers away. We saw the effects propagate very rapidly across the equator -- something quite unheard of in previous experience -- and move with the Southern Hemisphere jet stream to the east."

"By the time the first tendrils of dust ... had circumnavigated the Southern Hemisphere, which took about a week, separate storms were raging in three main centers. The most intriguing observation is that a regional storm in Claritas/Syria has been active every day since the end of the first week of July," said Malin.

Above: Images from the Mars Orbiter Camera on board MGS reveal a persistent active storm center in the Claritas/Syria region of Mars. [more images and information]

After three months, the air is finally beginning to clear on Mars. The planet's shrouded surface has cooled, allowing the winds to die down and the fine dust to begin settling. However, Mars is approaching the closest point of its orbit to the Sun (called perihelion). Mars will be at perihelion on October 12, 2001. Now that the atmosphere is beginning to clear, the return of unfiltered solar radiation could trigger additional high winds and kick up the dust all over again.

It's a prospect that some scientists welcome. Each storm presents its own telltale clues to the mystery of the Red Planet's dusty climate. A little more haze now could lift the veil on Martian storms yet to come....

Planet Gobbling Dust Storms -(Science@NASA) An enormous dust storm has exploded on Mars, shrouding the planet in haze and substantially raising the temperature of its atmosphere.

Mars Climate FAQ: What causes Martian dust storms? - from NASA/Ames

Stories about dust storms on Earth:

All the World's a Stage .... for Dust -- (Science@NASA) Tune in to a NASA website and watch giant dust clouds as they ride global rivers of air, cross-pollinating continents with topsoil and microbes.

The Pacific Dust Express -- (Science@NASA) North America has been sprinkled with a dash of Asia! A dust cloud from China crossed the Pacific Ocean recently and rained Asian dust from Alaska to Florida.

Right: In the upper frame a massive dust cloud swirls away from the Martian north pole. In the lower frame a similar-looking cloud blows westward over the Atlantic Ocean from Earth's Sahara Desert. Credit: Mars Global Surveyor (top) and SeaWiFs (bottom). [more]

More Mars Links:

Soviet Landers fall prey to Martian Dust - from ThinkQuest.org

Hubble's Best-ever Image of Mars: On June 26, 2001, the Hubble Space Telescope spotted a dust storm brewing in the Hellas Basin of Mars. A day later the storm erupted and became a global event.

Mariner 9 mission to Mars: NASA's Mariner 9 spacecraft arrived at Mars in 1971, right in the middle of a global dust storm.

Hubble images of Mars: from the Hubble Space Telescope Science Institute

Mars Orbiter Camera images: Close-up views of the 2001 Martian dust storm in visible light, from Malin Space Science Systems, Inc.

Thermal Emission Spectrometer: Scientists are using "TES" -- an Arizona State University-built instrument on board NASA's Mars Global Surveyor spacecraft -- to monitor thoing dust storm.

A Picture Gallery of Martian Dust Storms: from JPL's Mars Exploration web site