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Planetary News: Mars (2006)Mars Reconnaissance Orbiter "Sees" Opportunity as Rover Begins Long-Awaited ExplorationBy A.J.S. Rayl
In a week marred by Congressional scandals, Iraqi war casualties, and schoolhouse shootings, Earthlings almost had to go off planet to find any good news. But they only had to go as far as Mars . . . and what good news it was, accompanied by the best pictures taken from orbit yet. The Mars Exploration Rover (MER) Opportunity was into its first week collecting science at the much-anticipated, once-only-dreamed-about Victoria crater rim, when the Mars Reconnaissance Orbiter (MRO) cruised overhead last Wednesday and with its state-of-the-art camera photographed the rover from above, returning the picture in the first deluge of data to come from this, the latest of NASA's Mars missions. The High Resolution Imaging Science Experiment (HiRISE) camera with its stunningly powerful vision sent home one heck of a postcard -- an awe-inspiring picture that definitively shows Opportunity near the rim of Victoria crater on Mars with a resolution that actually defines the shape of the roving robot field geologist, as well as reveals its tracks. Even though the picture was technically only a test image, it was so good, the resolution so fine that it allowed Opportunity's mission planners to identify specific rover-scale targets of interest as they planned last Wednesday's drive -- a first in the exploration of Mars. The science phase of the mission officially begins November 8, after the 2-week solar conjunction ends (when Mars completes its orbit around the far side of the Sun from Earth), however, the teams working the 6 instruments onboard MRO were given 1 week to conduct tests and calibrations on their charges before conjunction begins in mid-October. If this first test data from HiRISE is to serve as any indication, MRO will easily live up to its promises. The HiRISE camera on MRO took the breath-taking picture last Wednesday (October 4, 2006), at 3:30 p.m. local Mars time, just about a week after Opportunity arrived at the rim. The Sun was about 30 degrees above the horizon and so illuminated the scene from the west. At the orbiter's altitude of 297 kilometers (185.6 miles) above the planet's surface, HiRISE is able to resolve objects that are 89 centimeters (35 inches) across.
HiRISE's compelling overview of Victoria crater shows the distinctive scalloped shape to its rim and in the full image one can clearly see in good detail the entire 800-meter (half-mile) Victoria crater, as well as the rover and its tracks and shadows, according to Alfred S. McEwen, HiRISE principal investigator for HiRISE, who released portions of the image at a NASA press conference in Washington, D.C., yesterday. The scallop-shaped is formed, the scientists say, by eroding crater wall material moving downhill. Layered sedimentary rocks are exposed along the inner wall of the crater, and boulders that have fallen from the crater wall are visible on the crater floor. A striking field of sand dunes covers much of the crater floor. "We're poised to have a fantastic mission, and we're not even at prime science mission yet," said McEwen, who works in the University of Arizona Lunar and Planetary Laboratory in Tucson, where the instrument team is headquartered. "This was our very first attempt to image 'off-nadir' (at an angle as opposed to straight down), and it worked fabulously well," he added. "It's been an exciting week." That may be something of an understatement.
"If you were a geologist driving up to the edge of a crater in your jeep, the first thing you would do would be to pick up the aerial photo you brought with you and use it to understand what you're seeing from ground level," pointed out Steve Squyres of Cornell University, principal investigator for both Opportunity and its twin, Spirit. That's exactly what they're able to do now with the HiRISE image with its incredible resolution. The new image from HiRISE on MRO adds significantly more detail compared to the once-amazing images from the Mars Orbital Camera (MOC) onboard the Mars Global Surveyor, which has been orbiting the Red Planet since 1997. But it cannot take away from the importance of those MGS images, which, after all, prompted the rover team to choose Victoria 2 years ago as the long-term destination for Opportunity because they showed the one-half-mile-wide crater's scalloped edges of alternating cliff ledges and gentler alcoves. During the past week, Opportunity followed the plan to drive north to the tip of the Cape Verde promontory, as announced in last month's MER Update, and is currently taking images of the crater interior. The MER team is naming the main features created by these scallops around the rim -- the kind of alcoves and the promontories that jut out from the rim -- after places that were visited by the Victoria during Magellan's expedition around the world. Victoria is 5 times larger than any crater Opportunity has visited during its Martian trek and the exposed geological layers in the cliff-like portions of the inner wall appear to offer up a much longer span of Mars' environmental history than the rover has studied in the smaller craters its visited. The high-resolution color images taken by Opportunity's panoramic camera (PanCam) since September 28 reveal previously unseen patterns in the layers, which Squyres described as "distinct variations" in the sedimentary layering as you look farther down in the stack. "That tells us the environmental conditions were not constant," he explained.
Within 2 months after landing on Mars in early 2004, Opportunity found geological evidence for a past environment that was wet. Scientists hope the layers in Victoria will provide new clues about whether that wet environment was persistent, fleeting, or cyclical. "What we see so far just adds to the excitement," added Jim Bell, also of Cornell, the lead scientist for the rovers' PanCams. "The team has worked heroically for nearly 21 months driving the rover here, and now we're all rewarded with views of a spectacular landscape of nearly 50-foot-thick exposures of layered rock."
The plan now is for Opportunity to drive from crater ridge to ridge, studying nearby cliffs across the intervening alcoves and looking for safe ways to drive the rover down. "It's like going to the Grand Canyon and seeing what you can from several different overlooks before you walk down," as Bell described it. The HiRISE image, along with others to come, will continue to help the team choose which way to send Opportunity around the rim, and where to stop for the best views. Conversely, the rover's ground-level observations of some of the same features will provide useful information for interpreting orbital images. "This is a tremendous example of how our Mars missions in orbit and on the surface are designed to reinforce each other and expand our ability to explore and discover," Doug McCuistion, director of the Mars Exploration Program in Washington DC, said at the press conference. "The ground-truth we get from the rover images and measurements enables us to better interpret features we see elsewhere on Mars, including very rugged and dramatic terrains that we can't currently study on the ground," McEwen elaborated. "But stay tuned," he added. "If you think the HiRISE image is spectacular, just wait." |
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