On firm dirt, Rover ready to paw Mars

With a flood of photos, scientists knew that they were once again on the surface of Mars.

They came like cosmic "Wish You Were Here" postcards on an early Thursday morning when scientific achievement seemed strangely like a slumber party. In crisp black and white, the images showed wheels caked in dust, intriguing rocks at arm's length, and the first tracks on a pristine landscape - all to the whoops of mission control.

After 11 anxious days of rotating and revolving to find the safest route off the lander platform, Spirit crawled the last nine feet Thursday of a 300-million mile journey to Martian soil. All told, the rover had been flung across space, scorched in the atmosphere, and then bounced 900 feet across the landscape in a protective shell of airbags.

At last, the most sophisticated machine in the history of human space exploration was ready to get to work.

It is a tool unlike any previously available to space scientists. Its Swiss-Army array of sensors and cameras, its microscope and grinding wheel - all mounted on a mobile rover - make for the best extraterrestrial geologist since Harrison Schmitt returned form the Moon on Apollo 17.

Already, the mission plan has become clear. Spirit will start cautiously before setting out on an ambitious journey within Gusev that could bring it to the lip of a smaller, dune-filled crater and up the slopes of a range of distant hills. With every opportunity, Spirit will scrape, sift, and claw in hope of finding evidence that water once filled the Connecticut-size bowl of Gusev crater beneath the Martian equator.

"This suite of instruments takes us to a scale of understanding of Mars rocks that we have never had before," says Albert Haldemann, a project scientist here at the Jet Propulsion Laboratory.

For the first few days, the instruments and the rover will merely orient themselves, taking rudimentary data and testing various systems - including the rover's robotic arm. In fact, the rover might not move again for at least a day or two. By the end of the weekend, though, scientists expect to begin the mission in earnest, making the daily decisions of where the best science might be and how to get to it.

"We're handing over the keys [to the scientists]," said engineer Chris Lewicki at a 3 a.m. press conference that often seemed more like an Oscar ceremony of speeches and "thank you's." "We got a chance to drive the car for a while, but in the end, we're just the valets driving the car around in front."

That process of simply moving from place to place is, in itself, a testament to the rover's advanced technology. In the first days, driver Brian Cooper and his colleagues will don 3-D glasses, look at the terrain on a computer screen, and stick a graphic lawn dart in the rock or hollow where scientists want to go.

While Pathfinder's Sojourner, NASA's 1997 Mars rover, had roughly 80 navigational commands to maneuver, Spirit has more than 850. The commands for each day will be written out while the rover sleeps during the Martian night, and typed into a computer program that interprets the directions for the rover before it moves an inch.

"While it's driving, we're asleep," says Dr. Cooper, who also piloted Sojourner in 1997.

Moreover, as time passes, the rover will "learn" to drive itself. Later in the mission, Cooper will simply direct the rover where to go and the rover itself will decide how to get there.

The list of things that Spirit can study is limited predominantly to rocks and soil. But Spirit's instruments were designed specifically to wring science from the smallest grain of dust or pattern in a rock.

"It's in the subtleties that all the information will come," says Bruce Betts, a scientist at the Planetary Society here.

Scientists have never had a thermal emission spectrometer on the surface of an extraterrestrial planet before, and its images could show traces of minerals that form with water. Spirit's grinding wheel can shave fractions of an inch off rocks, revealing older layers, and perhaps providing clues about what the region was like billions of years ago, when it was thought to be a lake. The microscopic imager will be the geologist's microscope, giving them a closer look at soils and minerals than ever before.

"It's amazing what a trained geologist can pick out," says Dr. Betts.

So far, the project scientists have their eyes on several prominent features east of the rover. As during Sojourner's mission, names are beginning to emerge. The large depression of wind-blown dust a short distance away is "Sleepy Hollow." Slightly nearer is the "Wasabi" rock pair, including one named "Sushi."

The rover will likely set off toward Sleepy Hollow, perhaps arriving there in a week to study soil samples. After that, it will move toward a crater 800 feet away. Its existence is a bit of geographical serendipity.

The one thing Spirit is not equipped to do is drill into the ground to look at deeper layers. The impact that caused the 650-foot-wide crater, however, has essentially done it for them. It sprayed the older and deeper dust and rock onto the surface, and scientists hope that evidence remains.

"As we drive toward it, we could see the progression of layers inverted," says Dr. Haldemann.

Once there, Haldemann and others envision peering into a depression perhaps more than 60 feet deep. If its sides are shallow, they might take Spirit inside.

With a top speed of just over 1.5 inches a second, Spirit isn't going anywhere fast, and its lifetime and range is anyone's guess. The original estimate was 90 days and 2,000 feet. Mission managers quietly expect more if all goes well. Yet the last item on their list could prove to be too great a challenge.

The mapping team estimates that a range of 300-foot hills lies roughly two miles east of Spirit. As the rover's mission winds down, it will turn toward them. Like a modern-day Tantalus story, Spirit will grow weaker and possibly die as the hills slowly fill more of its vision with intriguing vistas.

Chief scientist Steve Squyres boldly imagines views from a Martian hilltop, but even if Spirit ends up short, the trek could be one of the great dramas of space exploration. "It's going to be a shared adventure unprecedented in human history," Dr. Squyres said at a press briefing. "This is going to be a lot of fun."