Mars "Blueberries"

Photograph courtesy NASA/JPL-Caltech/Cornell/U.S. Geological Survey

"Blueberries," or iron-rich concretions, dot the Martian surface north of Victoria Crater. The Mars rover Opportunity found the spherules here and at its Eagle Crater landing site. Scientists theorize that a layer beneath the surface in these areas was once soaked with water long enough to form the spherules.