Figure 1
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This image of a target called "Private Joseph Field" combines four images from the microscopic imager on the robotic arm of NASA's Mars Exploration Rover Opportunity, with enhanced color information added from the rover's panoramic camera.

This target is within the "Marathon Valley" area of the western rim of Endeavour Crater. The component images were taken on May 29, 2016, during the 4,389th Martian day, or sol, of Opportunity's work on Mars. The mosaic shows an area spanning about 2 inches (5 centimeters).

Geochemical data indicate the presence of magnesium and iron sulfates at this location, most likely corresponding to the white pebble visible near the center of the image. These sulfates may have formed by the interaction of acidic fluids with the rocks along the rim of Endeavour crater.

JPL manages the Mars Exploration Rover Project for NASA's Science Mission Directorate in Washington. For more information about Spirit and Opportunity, visit http://marsrovers.jpl.nasa.gov.