PASADENA, Calif. -- NASAs Spirit Mars rover, now parked on the surface of Gusev Crater has deployed its robotic arm for the first time.

The arm is called the "instrument deployment device", or IDD.

Scientists were delighted at how well the Microscopic Imager is operating, taking extreme close-ups of the soil, showing the shape and size of particles.

"My personal view is that this is a conglomerate of dust particles on the surface of Mars," said Ken Herkenhoff, Science Lead for the Microscopic Imager from the U.S. Geological Survey in looking at first results. What holds the talcum powder-like particles together remains fodder for more study, he said.

Jessica Collisson, JPL Flight Director for the rover mission, said the arm will be used tomorrow to lower Spirits Mossbauer Spectrometer directly onto the surface. That instrument is to run for some four hours.

The device is built to determine with high accuracy the composition and abundance of iron-bearing minerals a way to decipher what early martian environmental conditions existed on the planet.

Later, the instrument robot arm is to be rotated, permitting use of the Alpha Particle X-Ray Spectrometer. That piece of gear will be positioned to hover over the soil and run for roughly 20 hours, Collisson said, determining the elements that make up rocks and soils.

Reports on how well the instruments worked, and what has been learned, is to be detailed Monday in the next press briefing. By that time, scientists and engineers should have decided on where next Spirit is to rove at Gusev Crater, and when use of a fourth instrument, a Rock Abrasion Tool, is planned.

Scientists have begun a detailed look at the rovers fresh tracks, created as Spirit crawled a short distance, away from the stationary lander hardware.

"The rover is not sinking in much at all," said Rob Sullivan, Science Team Member for the rover project from Cornell University. Both science and operational data can be gained from detailed looks at the rovers tracks, he said.

Sullivan said that during the rover mission at Gusev Crater, Spirit can be commanded to really attack the soil. Using a wheel of Spirit, the martian terrain can be excavated. Doing so, a trench can be dug into the soil in which the robots instruments can analyze subsurface materials.

"The more we mess up the soil around the rover, the more we learn," Sullivan said.

As Spirit steps up its scientific duties on the red planet, the robots identical twin -- Opportunity -- is screaming toward Mars. A key trajectory maneuver is set for late this evening, critical for targeting Opportunity to land eight days from now at Meridiani Planum, on the opposite side of the planet from where Spirit sits.

Ground controllers are slated to uplink commands to Opportunity between 2:00 p.m. to 5:00 p.m. Pacific Standard Times (PST), with the trajectory maneuver to start at 5:52 p.m. PST.

Joy Crisp, JPL Project Scientist for the Mars Exploration Rover effort, told SPACE.com that the maneuver later tonight will last around 9 seconds. That will tweak Opportunitys trajectory to precisely enter the martian atmosphere so it streaks toward its pre-selected landing point.

Dust storm activity elsewhere on Mars had impacted the upper atmospheric regions over Meridiani Planum. But that dust is settling out, Crisp said. That should mean clear sailing for Opportunity as it plummets to the surface and makes use of its landing system.

Mars Rovers: Complete Coverage

Astronomy for the Entire Family! Starry Night software brings the universe to your desktop. Map the sky from your location, or just sit back and let the cosmos come to you. LEARN MORE!