Clues to Wet History in Texture of a Martian Rock

This close-up view of a target rock called "Last Chance" was acquired by the microscopic imager on the arm of NASA's Mars Exploration Rover Opportunity on March 3, 2004, during the 39th Martian day, or sol, of Opportunity's work on Mars. The area covered in the view is about 2 inches (5 centimeters) across.

The embedded spherules evident in this image reminded researchers of berries in a muffin, so they were nicknamed "blueberries." These mineral concretions and other textures in this rock provided evidence about wet environmental conditions in the ancient past at Opportunity's landing site in the Meridiani Planum region.