This 3-D anaglyph, from NASA's Mars Exploration Rover Spirit, shows a circular imprint left in the Meridiani Planum soil by the rover's Moessbauer spectrometer. 3D glasses are necessary.

This 3-D image taken by the microscopic imager onboard the Mars Exploration Rover Opportunity shows a circular imprint left in the Meridiani Planum soil by the rover's Moessbauer spectrometer, an instrument located on its arm that detects iron-bearing minerals. Scientists are studying the curiously rounded grains for clues about the soil's history. The observed area is 3 centimeters (1.2 inches) across.

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