Rover Digs Mars

While NASA's Spirit rover was slowly picking its way across the martian surface, its twin rover was on the other side of the planet spinning its wheels — literally.

The Opportunity rover spun one of its wheels to dig into Mars, taking just minutes to excavate a 4-inch-deep trench that should open a window into the planet's past, scientists on the NASA mission said Tuesday.

"We dug a nice big hole on Mars," rover planner Jeffrey Biesiadecki told a news conference at NASA's Jet Propulsion Laboratory.

Opportunity sat parked on the gentle slope of a small crater while digging the 20-inch-long trench, an unprecedented maneuver that took six minutes of wheel spinning to complete.

The operation exposed material buried beneath the surface, including clotted chunks that could be seen protruding from the wall of the trench, said deputy main scientist Ray Arvidson, of Washington University.

The six-wheeled rover measured the mineralogy, texture and elemental composition of the trench site before digging and then began a second set of observations once it completed the task. Full results from the before-and-after measurements were expected Thursday.

Scientists chose the dig site because earlier observations revealed it is rich in an iron-bearing mineral called hematite, which typically forms in water.

Measurements should reveal if the mineral is limited to the surface or is present throughout the soil, Arvidson said. The scientific observations could also turn up traces of other minerals that might point to past water activity at the site.

Opportunity and its twin, Spirit, are searching for geologic evidence that Mars was once a wetter place hospitable to life.

Spirit, on the other side of Mars, continued its 1,150-foot trek to an impact crater. As of Tuesday, Spirit had traveled 356 feet, overtaking the 337 feet covered by the far smaller Sojourner rover during 1997's Pathfinder mission, project manager Richard Cook said.

Spirit could reach its destination in as little as 12 more days of driving, depending on how many stops it makes on the way to examine rocks flung out from the impact that created the crater, Arvidson said.

"The idea is to drive and look, drive and look," Arvidson said.