On Curiosity's 640th day (or sol) on Mars, as it continued its long drive to the base of Aeolis Mons (a.k.a. Mount Sharp), the robot stumbled across a fairly hefty meteorite. Shown here, the 2-meter-wide iron space rock can be seen embedded in the ruddy regolith.
The May 25 find adds to the puzzling reasons as to why the majority of meteorites found on the Martian surface are iron rich. On Earth, though fairly common, iron-rich meteorites are outnumbered by stony ones, leading scientists to believe that large iron-rich specimens may be more resistant to Martian erosion processes than stony space rocks.
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This large meteorite appears to consist of two separate components dubbed "Lebanon" (the larger meteorite) and "Lebanon B" (the smaller one in the foreground) by Curiosity's mission scientists.
Curiosity spent some time photographing and analyzing the meteorite with its Remote Micro-Imager (RMI), a component of the mission's Chemistry and Camera (ChemCam) instrument. The RMI images are the circular inserts in the image above. The rover's Mastcam instrument also imaged the area, adding color and context to the observation.
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Like other iron meteorites observed by Curiosity, and NASA's Mars Exploration Rovers Opportunity and Spirit, this example is riddled with pockmarks and cavities. According to a NASA news release, these features may be caused by "preferential erosion along crystalline boundaries within the metal of the rock." It's also possible that the cavities used to contain olivine crystals - often found in a rare type of stony-iron meteorites called pallasites. The olivine would have long since eroded away, leaving the iron behind.