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Guy Webster 818-354-6278 Jet Propulsion Laboratory,
News Release: 2007-029 March 14, 2007
NASA Mars Rover Churns Up Questions With Sulfur-Rich Soil
Some bright Martian soil containing lots of sulfur and a trace of water intrigues researchers who are studying information provided by NASA's Spirit rover.
"This material could have been left behind by water that dissolved these minerals underground, then came to the surface and evaporated, or it could be a volcanic deposit formed around ancient gas vents," said Dr. Ray Arvidson of
Determining which of those two hypotheses is correct would strengthen understanding of the environmental history of the Columbia Hills region that Spirit has been exploring since a few months after landing on Mars in January 2004. However, investigating the bright soil presents a challenge for the rover team, because the loose material could entrap the rover.
The bright white and yellow material was hidden under a layer of normal-looking soil until Spirit's wheels churned it up while the rover was struggling to cross a patch of unexpectedly soft soil nearly a year ago. The right front wheel had stopped working a week earlier. Controllers at NASA's Jet Propulsion Laboratory,
Due to the difficulty crossing that patch, informally named "Tyrone," the team chose to drive Spirit to a smaller but more accessible slope for the winter. Spirit stayed put in its winter haven for nearly seven months. Tyrone was one of several targets Spirit examined from a distance during that period, using an infrared spectrometer to check their composition. The instrument detected small amounts of water bound to minerals in the soil.
The rover resumed driving in late 2006 when the Martian season brought sufficient daily sunshine to the solar panels. Some of the bright soil from Tyrone was dragged to the winter site by the right front wheel, and Spirit spent some time measuring the composition and mineralogy of these materials. The material is sulfur-rich and consists of sulfate salts associated with iron, and likely calcium. "These salts could have been concentrated by hydrothermal liquid or vapor moving through the local rocks," said rover science team member Dr. Albert Yen, a geochemist at JPL. Two other patches of bright soil uncovered by Spirit before Tyrone were also sulfur-rich, but each had similarities to local rock compositions that were different at the three sites, suggesting localized origins.
Researchers will watch for more patches of bright soil. "If we find them along fractures, that would suggest they were deposited at ancient gas vents," Arvidson said. "If they are at the saddles between hills, that would suggest the deposits formed where groundwater came to the surface."
Scientists are describing recent findings by Spirit and Opportunity at the Lunar and Planetary Science Conference this week in
Spirit has driven away from the Tyrone area for a clockwise circuit around a plateau called "Home Plate." Researchers want to learn more about Home Plate, which Spirit visited briefly in early 2006. They are checking a hypothesis that explosive volcanism, driven by the interaction of magma with water, formed Home Plate and similar features.
Halfway around Mars,
"The images are breathtaking," said Dr. Steve Squyres of
The layers consist of sulfate-rich sandstone similar to other bedrock
"We found one group of cobbles that were clearly more resistant to erosion than the sulfate blocks thrown out onto the rim," Squyres said. "We checked the composition of one that we called Santa Catarina. Our suspicion now is that Santa Catarina is a piece of a meteorite." That would be the fifth meteorite found by the rovers.
More than three years into what was planned as a three-month mission on Mars, both Spirit and
JPL, a division of the California Institute of Technology,
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