* Panoramic view shows rust-colored surface strewn with gravel
* First 'self-portrait' reveals pebbles kicked up on top of craft
* NASA engineers prepare vehicle for four-day software upgrade
PASADENA, Calif., Aug 9 (Reuters) - The science rover Curiosity took a break from instrument checks on its third full day on Mars to beam back more pictures from the Red Planet, including its first self-portrait and a 360-degree color view of its home in Gale Crater, NASA said on Thursday.
The panoramic mosaic, comprising 130 separate images that Curiosity captured with its newly activated navigation cameras, shows a rust-colored, pebble-strewn expanse stretching to a wall of the crater's rim in one direction and a tall mound of layered rock in another.
That formation, named Mount Sharp, stands at the center of the vast, ancient impact crater and several miles from where Curiosity touched down at the end of an eight-month voyage across 352 million mile (566 million km) of space.
The layers of exposed rock are thought to hold a wealth of Mars' geologic history, making it the main target of exploration for scientists who will use the rover to seek evidence of whether the planet most similar to Earth might now harbor or once have hosted key ingredients for microbial life.
But mission controllers at the Jet Propulsion Laboratory near Los Angeles are exercising caution immediately following Curiosity's jarring, death-defying descent to the surface on Sunday night.
They plan to spend weeks putting the nuclear-powered, six-wheeled rover and its sophisticated array of instruments through a painstaking series of "health" checks before embarking on the thrust of their science mission in earnest.
The $2.5 billion Curiosity project, formally named the Mars Science Laboratory, is NASA's first astrobiology mission since the Viking probes of the 1970s and is touted as the first fully equipped mobile geochemistry lab ever sent to a distant world.
EQUIPMENT CHECKUPS
After three full days on the Red Planet, "Curiosity continues to behave flawlessly" and has "executed all planned activities" without a hitch, mission manager Michael Watkins said at a JPL news briefing.
The latest round of equipment checks included an instrument designed to determine mineral composition of powdered rock and soil samples; one to analyze soil and atmospheric samples for organic compounds; one to detect traces of water locked in shallow mineral deposits; and another that uses particle X-rays to identify chemical elements in rocks and soils.
The very delivery of Curiosity to the surface of Mars already has been hailed by NASA as the greatest feat of robotic spaceflight.
The car-sized rover, which flew from Earth encased in a protective capsule, blasted into the Martian sky at hypersonic speed and landed safely seven minutes later after an elaborate, daredevil descent combining a giant parachute with a rocket-pack that lowered the rover to the Martian surface on a tether.
Since then, the rover has been sending a string of early images back to Earth, relayed by two NASA satellites orbiting Mars, providing glimpses of a terrain that scientists say appear reminiscent of the Mojave Desert in Southern California.
One shot beamed back late Wednesday night, the first taken by Curiosity of itself, shows the rover's top deck strewn with dark pebbles apparently kicked up from the ground when the craft landed. NASA scientists said the gravel does not appear to pose any risk to instruments on the vehicle.
Two separate high-resolution "Navcam" images taken of the surface show that thrust from the sky-crane rockets during descent carved out a 1.5-foot (0.5-meter) trench in the surface, exposing what appears to be Martian bedrock underneath.
When Curiosity wakes up for its fourth day on Mars, early Friday California time, mission controllers plan to conduct additional instrument checks and prepare the craft for an upgrade of its main computer software for surface operations. All other activities will be suspended during that upgrade, which will begin on day 5 of the mission and last four days. (Reporting by Steve Gorman; Editing by Anthony Boadle)
