This image from the front hazard-avoidance camera on NASA's Mars Exploration Rover Opportunity shows rover wheel tracks on the inner slope of 'Endurance Crater.' Opportunity took the image on Aug. 4, 2004.

This picture from the front hazard-avoidance camera on NASA's Mars Exploration Rover Opportunity shows rover wheel tracks on the inner slope of "Endurance Crater." Opportunity took the image on sol 188 (Aug. 4, 2004), before transmitting it and other data to the European Space Agency's Mars Express orbiter. The orbiter then relayed the data to Earth.

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