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| A trench dug by Opprtunity's right front wheel reveals bright areas below the surface. Finding out what they are will be the next job for the rover's cameras and spectrometers Click on the image for a high-resolution version (1431 x 953 pixels, 794K) |
The tool is actually the rover's set of six wheels, any one of which can be spun backwards or forwards to dig a trench to examine the geology of the rocks and soils beneath the surface. Opportunity's right front wheel, perched on a 9-degree downward slope in a crater, was used to dig a trench 20 centimeters (8 inches) wide, 50 centimeters (20 inches) long and 10 centimeters (4 inches) at its deepest part.
Cornell University researchers helped perfect the digging method in which all but one of a rover's wheels is locked in place. The remaining wheel is then spun, trenching the surface soil and enabling the remote study of the soil's stratigraphy and an analysis of whether water once existed.
For controllers at the Jet Propulsion Laboratory (JPL) in Pasadena, the process involved complicated maneuvers -- a "rover ballet," according to Rob Sullivan, the Cornell researcher and member of the Mars mission science team who helped develop the trenching mechanism with Harry Stewart, Cornell associate professor of civil engineering, and JPL engineers. Indeed, controllers had to send the rover 66 "mobility commands."
At a press conference at JPL today (Feb. 17) Sullivan described the eight black-and-white images taken by the rover's hazard identification cameras, showing "clotty" soil along the upper walls of the trench and "contrasts in brightness between brighter floor material and material outside of the trench on the plain."
"We're not sure of the cause of that," Sullivan said. "It could be the material itself is intrinsically brighter than the stuff seen on the surface." Or, he said, "it could be that we have discovered something that is intrinsically different down on the floor of this trench than we have seen so far on the surface."
In the next couple of days, the rover will back away from the trench and take high-resolution color images with its mast-mounted Pancams, or panoramic cameras. The trench also will be examined by the rover's microscopic imager, particularly the clotting of soil on the walls. Opportunity's Mössbauer spectrometer also will take a look at the soil composition and compare it with data from the same spot before the trench was dug. The science team, Sullivan said, now contemplates spending an extra day at the trench.
Opportunity took the "very difficult, spectacular" 11-meter drive along the slopes of its landing site inside a crater in the Meridiani Planum to reach an area that its miniature thermal emission spectrometer had identified as rich in hematite, a mineral often associated with the presence of water. The purpose of the trenching, Sullivan said, was to see if hematite is intrinsic to the area and can be found at depth as well. However, he noted, there is as yet "no evidence to suggest clumps of hematite" in the area.
Each rover wheel is carved from aluminum blocks, and inside each wheel hub is a motor. To spin a wheel independently, JPL operators simply switch off the other five wheel motors. Sullivan, Stewart and Cornell undergraduates Lindsey Brock and Craig Weinstein used Cornell's Takeo Mogami Geotechnical Laboratory to examine various soil strengths and characteristics. They also used Cornell's George Winter Civil Infrastructure Laboratory to test the interaction of a rover wheel with the soil. Each rover wheel has spokes arranged in a spiral pattern, with strong foam rubber between the spokes; these features help the rover wheels function as shock absorbers while rolling over rough terrain on Mars.
In the future for Opportunity, press conference panel member Ray Arvidson, deputy project manager, said is a climb up the sides of the crater and over the rim and then a 600-meter drive east to another crater.
Meanwhile, Opportunity's twin rover, Spirit, which has spent nearly 44 days in the Gusev crater on the opposite side of Mars, is making good progress toward the crater nicknamed "Bonneville." The first driving session on Monday covered 19 meters (62.3 feet). After a rest, Spirit continued another 8.5 meters (27.9 feet) in the afternoon, resulting in a total drive of 27.5 meters (90.2 feet), a new one-sol record. The remaining distance to "Bonneville" is about 245 meters (about 800 feet) from Spirit's new location.