On December 9, 2004, NASA's Mars Exploration Rover Spirit brushed dust from the surface and took these magnified images of this rock dubbed Wishstone.
The 5-centimeter circle seen here with the microscopic imager showed darker pieces of material randomly distributed within lighter-colored grains.
January 4, 2013 12:41 PM PST
Photo by: NASA/JPL/Cornell/USGS
| Caption by: James Martin
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