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NASA uses Gusev Crater
Scientists already are putting together a portrait of Spirit's new home in Mars' 100-mile-wide Gusev Crater. What they're finding is a site that, so far, fits their hypothesis: The crater, which strongly resembles an ancient lakebed, might have held water. "We couldn't have hoped for a better site," said Nathalie Cabrol, a planetary scientist at NASA Ames Research Center who was instrumental in getting Gusev on the rovers' itinerary. Cabrol said seeing the first picture of Gusev was like meeting someone she'd been corresponding with by mail for 15 years. "It got very emotional at that point," she said. She and other scientists are looking closely at the first pictures Spirit took. They already know a few things: Small, round depressions, possibly craters, are nearby. The landscape is criss-crossed by dust-devil tracks that, helpfully, have stripped dust away from the surface. The rocks are perfect for study and not big enough to stop the rover from driving through them. "We have the rocks we wanted . . . right in front of us," Cabrol said, "and very tempting hills just far away enough, so that we know we can go there, because it's flat enough." "I'm intrigued by how very flat it is," principal investigator Steve Squyres said. "That sort of looks like what you would expect a lake bed to look like. I'm intrigued by the rock distribution, the shortage of big boulders. . . . I'm intrigued by those holes in the ground and how they might provide us access to stuff underneath the surface." For now, the pictures raise more questions than they answer, Squyres said. The scientists will know a lot more when Spirit rolls off its lander and starts digging into the soil and rocks, probably in a week. Spirit landed about 6 miles away from the bull's-eye in its landing ellipse -- a shift that proved to be exactly the area where the science team wanted to go, Squyres said. The spacecraft shot three descent images on the way down. It quickly compared high-contrast elements in the images - in this case, a distinctive cluster of craters -- and fired small rockets to compensate for a drift caused by high winds. More helpful for the science team, the descent images, when compared with more expansive photos taken of the region by the orbiting Mars Global Surveyor, give them some geographical context for the landing site. For instance, the Surveyor image shows the area is streaked with dust-devil tracks. Dust devils on Mars strip away dust from the surface, leaving exposed areas that are more accessible to the rover. They also raise the intriguing possibility that Spirit might actually see afternoon dust devils as it drives around. "These things could do terrific atmospheric science as well," Squyres said of the rovers. "The dust devils have done us a favor by cleaning off our rocks for us, and I'd like to catch one in the act." One area where dust -- or at least a fine material -- seems evident is in the large depression front and left of the rover. The round hole seems to be filled with a soft material. "I don't know for sure it's not a rover trap," Squyres said. "And we're going to have to be a little bit cautious." The depression's lip suggests it might be an impact crater. Craters are appealing targets for the rovers, because when objects hit the surface, they kick up rocks. In effect, impacts do some of the digging, unearthing deeper, older material that could provide evidence of water. "It's the whole ball game in Gusev," Cabrol said, "because it's an old place, and it might be a lakebed . . . but the lakebed might be a hundred meters beneath our feet and covered by something else." Many of the rocks visible in the images could be material ejected from impacts, Cabrol and Squyres said. The landscape is very different from anything the Viking landers or the Pathfinder Sojourner saw, Cabrol said. "The distribution of rocks is very different from anything we've seen and, once again, is very consistent with a sedimentary basin," she said. "And the other thing that struck me is the sheer beauty of the place and the poetry of this place."
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