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Planetary geology
Mars’ lost landers

Researchers working with NASA’s Mars Global Surveyor announced that they may have found something they’ve been looking for: the sites where two Mars landers settled, several decades apart.

Over the past few years, the team previously identified and photographed Viking 1, the Mars Pathfinder lander, and the two Mars Exploration Rovers, Spirit and Opportunity. Now they may have found Viking 2, which landed unobserved in 1976, and the Mars Polar Lander, lost in a crash-landing in December 1999.

Viking 2 touched down on Mars’ surface on Sept. 3, 1976, but its exact location could not be confirmed until now, according to Malin Space Science Systems, the company that built and runs the Mars Orbital Camera aboard the Mars Global Surveyor. According to the company’s announcement on May 5, finding the lander was challenging “owing to the extreme subtlety of horizon features visible in the lander panoramas and relatively inaccurate radio tracking data.” But estimates using sightlines from the lander’s pictures allowed the team to point the Mars Orbiter Camera toward a location on the Utopia Planitia, “amid remarkably homogenous terrain,” where they found a shape that appears to match the calculated orientation of Viking 2.

The team is less certain of its identification of the Mars Polar Lander. Lost after a communications failure scrambled its ability to navigate during touchdown, the lander disappeared without a trace. At 6 meters long, finding the small shiny object would be difficult at the Mars Orbital Camera’s resolutions. Using a modified imaging technique, the team started with the Mars rovers’ landing sites as points of comparison for what the Mars Polar Lander site could look like. The rovers’ parachutes were made of similar materials to the polar lander’s, and their rockets would have disturbed the soil upon arrival.

That knowledge has led to tentative confirmation of a candidate site found in 2000, which contains what look to be the Mars Polar Lander’s parachute and rocket-blast “skid marks.” The team will be checking the site for more definitive evidence that the object landed there, including the tiny “dot” of the lander itself. Confirmation of the landing site may give researchers more information about what exactly went wrong with the Mars Polar Lander.

Another instrument that will join the search is the Mars Reconnaissance Orbiter, scheduled to launch in August and begin orbiting Mars in 2006. Researchers on that mission will be keeping an eye out for the Mars Polar Lander, as well as for the British lander Beagle 2, which disappeared after entering Mars’ atmosphere on Dec. 25, 2003.

Naomi Lubick

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