A magnified look at the martian soil near the Mars Exploration Rover Opportunity's landing site, Meridiani Planum. The image was taken by the rover's Microscopic Imager. Scientists are intrigued by the spherical rocks, which can be formed by a variety of geologic processes, including cooling of molten lava droplets and accretion of concentric layers of material around a particle or seed. Credit: NASA/JPL/Cornell Click to enlarge.
