The rock abrasion tool (RAT) on NASA's Mars Exploration Rover Spirit ground two holes in a relatively soft rock shown here near the base of the "Columbia Hills" field site on Mars. This approximate true-color Pancam image (generated using the camera's 600-, 530-, and 480-nanometer filters) taken on sol 200 (July 25, 2004) shows the natural red and reddish-brown color of the rock. Scientists speculate that this relatively soft rock (compared to others analyzed by Spirit) may have been modified by water. Small cracks in the surface outside the drill holes may be the result of interactions with water-rich fluids.

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