NASA's Spirit rover (search) reached out to Mars on Friday, extending its robotic arm for the first time to snap a series of tight close-ups with a combination microscope and camera that reveal the rust-colored soil of the planet in unprecedented detail.

The mostly black-and-white images show a tiny area, 1.44 inches square, that includes clumps of fine particles that may be stuck together by the martian equivalent of Epsom salts. The images show features nearly as small as the diameter of a human hair.

"This is the highest resolution by far we have ever seen Mars at," said Ken Herkenhoff, of the U.S. Geological Survey (search), and the lead scientist for the microscopic imager on Spirit.

Several of the new images were taken by Spirit's fisheye, hazard-avoidance cameras that show the rover's robotic arm extended for the first time. The arm is about the same length as an adult human's arm, giving the rover broad reach to probe its immediate surroundings.

Spirit turned its attention to the silty ground beneath its six aluminum wheels within a day of rolling onto the planet's surface on Thursday, 12 days after arriving from Earth. Spirit should spend three more days parked beside its lander doing science work.

Scientists picked a pebble-free area to begin characterizing the soil that dominates the immediate landscape. Spirit landed in a region that is rich in dirt with a few rocks.

Tiny ring-shaped features appear in the microscopic images that may be evidence of minute amounts of water reacting with minerals in the martian soil, said John Grotzinger, of the Massachusetts Institute of Technology, and a member of the rover science team.

Over the weekend, NASA (search) planned for the rover to use two German-made instruments, its Mossbauer and Alpha Particle X-ray spectrometers, to analyze the minerals and chemistry of the martian soil.

Both instruments share space on Spirit's robotic arm with the microscopic imager and a rock abrasion tool, which can grind away at martian rocks to reveal their insides for study.

Early next week, the robot should set off on a zigzagging path to prospect for further geologic evidence that the now-dry planet was once wetter and hospitable to life.

Spirit's twin, Opportunity, is scheduled to land Jan. 24 on the opposite side of the planet.

On Friday, NASA trimmed Opportunity's course, firing the spacecraft's rockets three times for a total of 30 seconds to put it on track to land within its target ellipse.