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"We think we have a rock similar to something found on Earth," said Dr. Benton Clark of Lockheed Martin Space Systems, Denver, USA, science-team member for the Opportunity and Spirit rovers on Mars. The similarity seen in data from Opportunity's alpha particle X-ray spectrometer "gives us a way of understanding 'Bounce Rock' better," he said. Bounce Rock is the name given to the odd, rugby ball-sized rock that Opportunity struck while bouncing to a stop inside its protective airbags on landing.
The comparison helps resolve a paradox about the meteorites. Bubbles of gas trapped inside these meteorites match the Martian atmosphere so closely that scientists have been confident for years that they originated from Mars. However, examination of rocks on Mars with orbiters and surface missions had never found anything like them, until now.
"There is a striking similarity in spectra," said Christian Schroeder, a rover science-team collaborator from the University of Mainz, Germany, which supplied both Mars rovers' Moessbauer spectrometer instruments for identifying iron-bearing minerals. Mars Exploration Rover scientists described two meteorites in particular during a recent news conference. One, named Shergotty, was found in India in 1865 and it gave its name to a class of Martian meteorites called shergottites.
A shergottite named EETA79001 that was found in Antarctica in 1979 has a composition very close to that of Bounce Rock's. Those two and about 18 other meteorites found on Earth are believed to have been ejected from Mars by the impacts of large asteroids or comets hitting the Martian surface.
Opportunity's miniature thermal emission spectrometer indicates that Bounce Rock contains a volcanic mineral called pyroxene. The high proportion of pyroxene makes it unlike other rocks studied by Opportunity and its twin, Spirit. Thermal infrared imaging by the NASA orbiter Mars Odyssey, suggests a possible origin for Bounce Rock. An impact crater about 25 kilometres wide and about 50 kilometres southwest of Opportunity. The images show that some rocks were thrown outward by the crater forming impact.
Opportunity plans to drive eastward toward a closer crater dubbed "Endurance" that might offer access to thicker exposures of bedrock for the rover to examine. Engineers believe that new software, uploaded last week, will improve mobility performance and the rover may reach Endurance within two weeks.
More info: Mars Rovers at JPL
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