This image of small spherules on the surface of Mars near Fram Crater was taken by NASA's Opportunity rover in April 2004. The area shown is 1.2 inches (3 centimeters) across. These are examples of the mineral concretions that have been nicknamed "blueberries." Opportunity's investigation of these hematite-rich concretions have provided evidence that water may have once flowed on the Martian surface. Similar formations have been found on Earth near bodies of water.
NASA / JPL-Caltech / Cornell / USGS