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| This approximate true-color panoramic camera image, taken by the Mars rover Spirit and calibrated and assembled in Cornell's MarsLab, shows a rock outcrop dubbed "Longhorn," and behind it, the sweeping plains of Gusev Crater. On the horizon, the crater's rim is clearly visible. The view is to the south of the rover's current position. On Aug. 18, Cornell's Steve Squyres, leader of the Mars mission science team, noted that now Spirit is finally examining bedrock in the "Columbia Hills," it is finding evidence that water thoroughly altered some rocks in Gusev Crater. NASA/JPL/Cornell |
It has taken Spirit half a year of driving across the massive crater's floor to reach the hills and finally to touch bedrock. Now, Spirit's initial inspection of an outcrop called "Clovis" on a hill about 9 meters (30 feet) above the plain suggests that water might once have been active at Gusev.
"We have evidence that interaction with liquid water changed the composition of this rock," said Steve Squyres, priofessor of astronomy at Cornell and principal investigator for the science instruments on Spirit and its twin rover, Opportunity, which is investigating a deep crater on the opposite side of Mars. "This is different from the rocks out on the plain, where we saw coatings and veins apparently due to effects of a small amount of water," said Squyres. "Here, we have a more thorough, deeper alteration, suggesting much more water."
Speaking at a media briefing at the Jet Propulsion Laboratory in Pasadena, Calif., Squyres said, "To really understand the conditions that altered Clovis, we'd like to know what it was like before the alteration. We have the after. Now we want the before. If we're lucky, there may be rocks nearby that will give us that."
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| This approximate true-color panoramic image, taken by the Mars rover Spirit and processed in Cornell's MarsLab, shows the rock outcrop dubbed "Clovis." The rock was discovered to be softer than other rocks studied so far at Gusev Crater after the rover easily ground a hole into it with its rock abrasion tool. An analysis of the interior of the hole with the rover's scientific instruments indicate that Clovis has been chemically altered, and that fluids once flowed through the rock. NASA/JPL/Cornell Click on the image for a high-resolution version (1.1MB) |
Spirit struggled mightily to reach Clovis, overcoming the challenge of rough, steep terrain and subsequent backsliding. The site is near the crest of the "West Spur" of "Columbia Hills."
Last January Opportunity landed right beside exposed bedrock and promptly found evidence there for an ancient body of saltwater. On the other hand, Doug Ming, a rover science team member from NASA's Johnson Space Center, Houston, said yesterday, indications of water affecting Clovis come from analyzing the rock's surface and interior with Spirit's alpha particle X-ray spectrometer and finding relatively high levels of bromine, sulfur and chlorine inside the rock. He said, "This is also a very soft rock, not like the basaltic rocks seen back on the plains of Gusev Crater. It appears to be highly altered."
Squyres has noted that the mission is not trying to prove that water once flowed across the Martian surface, evidence of which was discovered by Mariner 9 in 1971. Instead, the mission is seeking to find rocks that were actually formed in liquid water so that it will be possible to read the record in those rocks to learn something about what the environmental conditions were like and if they would have been suitable for life.
On Opportunity, a tool for exposing the insides of rocks stopped working on Sunday, Aug. 15, but engineers are optimistic that the problem that can be fixed soon. The most likely diagnosis: a pebble trapped between the cutting heads of the rock abrasion tool.
Opportunity has completed a transect through layers of rock exposed in the southern inner slope of stadium-sized "Endurance Crater." The rocks examined range from outcrops near the rim down through progressively older and older layers to the lowest accessible outcrop, called "Axel Heiberg" after a Canadian Arctic island.
Small, gray stone spheres nicknamed "blueberries" are plentiful in Endurance just as they were at Opportunity's smaller landing-site crater, "Eagle." Pictures from the rover's microscopic imager show a new variation on the blueberries throughout a reddish-tan slab called "Bylot" in the Axel Heiberg outcrop. "They're rougher textured, they vary more in size, and they're the color of the rock, instead of gray," said Zoe Learner, a science team collaborator from Cornell. "We've noticed that in some cases where these are eroding, you can see a regular blueberry or a berry fragment inside." One possibility is that a water-related process has added a coarser outer layer to the blueberries, she said, adding, "It's still really a mystery."
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