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29 June 2007
NASA Rover To Descend into Massive Martian Crater
Geologic exploration will open window into planet's ancient environment
Washington -- One of NASA's robotic explorers, Opportunity, is about to descend into one of the largest craters on Mars, opening a window for scientists into the ancient environment of the fourth planet from the sun.
Opportunity and its twin rover Spirit have been exploring the planet since 2004, when they began what NASA scientists planned as 90-day missions.
The missions have been extended four times and, though both rovers are well past their design lives and have had some mechanical problems, their instruments are working and they continue to send science data back to Earth.
Opportunity reached the Victoria Crater nine months ago and has been driving clockwise around the jagged rim, along its pattern of alcoves and promontories, collecting images of the crater walls to survey the geology and find the best way into the crater.
Scientists at NASA's Jet Propulsion Laboratory and the Science Mission Directorate at NASA headquarters authorized the rover's descent into the crater despite potential risks.
"The kind of stuff we want to do in this crater requires a healthy six-wheel vehicle, which is what we have now," said Steven Squyres of Cornell University in New York, principal investigator for the Mars Exploration Rover’s science instruments, at a June 28 NASA briefing.
"What we're interested in doing is getting in there, doing our business and getting out while the vehicle still has the six wheels to enable us to climb out," he added. "So if we're ever going to do it, now's the time."
The other rover, Spirit, lost the use of one wheel more than a year ago, affecting its ability to climb but not to drive on flat surfaces.
"Given that this mission is 12 times further along than they initially bargained for, and the great success of it," said Alan Stern, NASA associate administrator for the Science Mission Directorate, "if we were to end up stuck in that crater, the risk is worth the reward."
ANCIENT ENVIRONMENT
Opportunity will drive into Victoria Crater July 7 or July 9, said John Callas, Mars Exploration Rover project manager at JPL, through an alcove named Duck Bay.
This and other areas of the crater are named after places that Ferdinand Magellan and his crew visited on their first circumnavigation of Earth from 1519 to 1522. Victoria was the name of one of his five ships.
Opportunity's only identified goal so far is to collect a sample of a geologic feature of the crater wall.
Showing a photograph of a promontory called Cape St. Vincent, Squyres said the wall has three different geologic units. One is a top unit of sand and jumbled material that was thrown out of the crater during a meteor impact millions of years ago. Another, the lowermost, is a unit of bedrock that is the original pre-impact surface of the planet.
"But the thing that really caught our eye," Squyres said, "and this is visible all the way around the crater like a bathtub ring, is a band of bright material at the top of the bedrock. It's less than a meter thick and it's distinctly bright and weathers differently and is somehow different from everything else around it."
The bright band was in contact with the Martian atmosphere at the time Victoria Crater was formed and, he added, "may preserve in its details information about the interaction of the rocks with the ancient Martian environment."
SPIRIT
Meanwhile, on the other side of the planet, Spirit analyzed a patch of Martian soil so rich in silica that it might provide some of the strongest evidence yet that ancient Mars was much wetter than it is now.
Silica is silicon dioxide. On Earth, it commonly occurs as the crystalline mineral quartz and is the main ingredient in window glass. The Martian silica Spirit found is noncrystalline, with no detectable quartz.
In most cases, the rover scientists said, water is required to produce such a concentrated deposit of silica. A possible origin could have been the interaction of soil with acidic steam produced by volcanic activity, or from water in a hot spring.
The finding, said Doug McCuistion, director of NASA's Mars Exploration Program, in a May 21 statement, "reinforces the fact that significant amounts of water were present in Mars' past, which continues to spur the hope that we can show that Mars was once habitable and possibly supported life."
Because one of Spirit's six wheels no longer rotates, it leaves a deep track as it drags through soil. That churning has exposed several patches of bright soil, leading to some of Spirit's biggest discoveries at Gusev Crater, including this recent discovery. (See related article.)
The team has laid out plans for further study of the soil patch and surrounding deposits.
More information about the Mars rovers and crater images are available on the NASA Web site.
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