Mars Index - Top Ten MER Images - Top Raw Images
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This panoramic image shows the front face of a rock outcrop criss-crossed by parallel lines from left to right, covered with millimeter-scale round concretions, and surrounded by fine-grained sand.
The Texture of 'El Capitan'
03/02/2004
Opportunity
Rising majestically above the Texas desert, El Capitan on Earth formed from an ancient marine fossil reef. The much smaller martian rock doesn't boast signs of ancient life, but is celebrated for providing key evidence that Eagle Crater was once covered in water.
This image, taken by the panoramic camera on the Mars Exploration Rover Opportunity, shows a close up of the rock dubbed "El Capitan," located in the rock outcrop in "Eagle Crater" at Meridiani Planum, a bit right of center, in the upper portion of the outcrop. El Capitan was named after the most dramatic peak inside Guadalupe National Park in Texas. El Capitan was a significant find on Mars due to the multiple ways it provided clues to lead scientists to believe the entire outcrop in Eagle Crater was once covered in water.

This image shows fine, parallel lamination in the upper area of the rock, which also contains scattered sphere-shaped objects ranging from 1 to 6 millimeters (.04 to .24 inches) in size. There are also more abundant, scattered vugs, or small cavities, that are shaped like discs. These are about 1 centimeter (0.4 inches) long. The rover's miniature thermal emission spectrometer uses infrared detectors to determine the mineral composition of rocks and soil. The miniature thermal emission spectrometer showed that "El Capitan" contains a considerable amount of sulfate. Another science tool, the German-built Mössbauer spectrometer identified the mineral jarosite, which contains water in the form of hydroxyl.

Image Credit: NASA/JPL/Cornell