Mars Index - Top Ten MER Images - Top Raw Images
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Extending from the upper left corner to the lower right corner of this microscopic image are four flat layers of rock, tilted at an angle from the camera, measuring 3 centimeters (1.2 inches) wide. Between each layer is a horizontal gap where rock material has been weathered away. On top of one of the layers is a small, round concretion about 2 millimeters (0.08 inch) wide.
Buried Treasure
Hidden within the weathered confines of age-old layers lies a small, simple sphere more precious to Mars scientists than gold: a remnant sign of ancient water on the red planet.

Image Credit: NASA/JPL/Cornell/USGS