On the surface of Mars, 300 million miles from earthlings, NASA's robotic rover Spirit extended its arms for the first time to snap extraordinary close-ups of the planet's rust-colored soil.

  The images showed features nearly as small as the diameter of a human hair.

The new black-and-white images taken by the microscope-camera lens show a tiny area, 1.44 inches square, with clumps of fine particles that may be stuck together by the martian equivalent of Epsom salts.

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

Images released by NASA during a news conference at the Jet Propulsion Laboratory (search) include several taken by Spirit's fisheye, hazard-avoidance cameras, which show the rover's robotic arm extended for the first time.

The arm, which is about the length of an adult human's arm, gave the rover broad reach to probe its immediate surroundings even while parked.

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

Scientists picked a pebble-free area to begin examining 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, who is 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. NASA plans for Spirit, designed to travel dozens of yards a day, to begin heading toward a crater about 825 feet away.

Spirit's twin, Opportunity, is scheduled to land Jan. 24 on the opposite side of the planet, and NASA wants to park the Spirit rover for the three days immediately following the new rover's arrival so controllers involved in the $820 million double mission can focus on Opportunity.

NASA trimmed Opportunity's course late Friday, firing the spacecraft's rockets three times for a total of 30 seconds to put it on track to land within its target ellipse. NASA plans to skip two other chances to adjust Opportunity's path unless needed, JPL spokesman Guy Webster said. The so-called trajectory correction maneuvers help steer a spacecraft to its destination and are akin to the multiple strokes a golfer typically makes when playing a hole.