The Mars rover Opportunity is investigating the inner walls of the crater in which it landed and finding some intriguing characteristics. "This is wild looking stuff," remarks principal investigator Steve Squyres of Cornell University. "The rock is being eroded away and these spherical grains are dropping out."

Using its microscopic cameras and onboard spectrometers, the robot beamed back data about the Martian bedrockdubbed Opportunity Ledge--to its earthbound controllers. Up close, the buff-colored outcrop rock is finely layered and is being eroded by windblown sand, the researchers report. "Embedded in it like blueberries in a muffin are these little spherical grains," Squyres says. There are two possible explanations for their formation, he notes. They could have formed out of molten rock that was thrown into the atmosphere by an extreme event such as a volcano or an impact with a meteorite. Alternatively, they could be concretions of minerals that came out of solution as water moved through the rock. Further information and analysis will be required to determine which of these scenarios is correct.

Meanwhile Opportunitys twin, Spirit, has rebounded from the memory malfunction that sidelined it from January 21 until the beginning of February. After successfully drilling into the rock dubbed Adirondack, Spirit was on the move again and hit a milestone early Tuesday morning by traveling the farthest distance in one day on Mars. On its 37th sol on the Red Planet, Spirit covered 21.2 meters--shattering the previous one-day record of seven meters set by the Mars Sojourner rover--on its way to Bonneville Crater.