ROCK FESTIVAL ON MARS

By LEON JAROFF

Barnacle Bill. Yogi. Casper. Scooby Doo. Flat Top, Boo-Boo. The Couch. Souffle. After billions of years of anonymity, a motley collection of rocks on the Martian flood plain called Ares Vallis at last had names of their own. And back on Earth last week, the Pathfinder scientists who had playfully nicknamed the rocks were enjoying, as one of them phrased it, "a rock festival," reveling in the torrent of data being yielded by the rock stars and their surroundings.

Indeed, after only a week on the surface of Mars, Pathfinder had conducted dozens of worthy science experiments, had begun to challenge at least one long-held perception about the red planet and had transmitted more than 1,700 photos of the landscape, many of which were incorporated into a "monster pan," a spectacular 360[degrees], three-dimensional, horizon-to-horizon mosaic image that, when viewed through 3-D glasses, is almost as good as being there. The mission had also achieved a historic first on Mars: a motor-vehicle accident.

The undisputed star of the week, however, surpassing even the rocks, was the 25-lb. Sojourner, which Rob Manning, Pathfinder's flight-systems chief engineer, dubbed "The Little Rover That Could." Having inched its way down the steeply inclined lander ramp, the six-wheeled Sojourner crept gingerly onto the Martian surface early last week and, in its first official scientific experiment, shoved the nose of its X-ray spectrometer into the dust at the foot of the lander.

After bombarding the reddish dirt with helium nuclei and analyzing the resulting patterns of radiation, the spectrometer revealed that the soil was rich in iron and virtually identical to that examined at other sites 21 years earlier by the Viking landers. This suggested to scientists that Martian topsoil is widely distributed by the planet's frequent global dust storms. Why the reddish hue? "The surface of Mars is rusting," explains Jim Bell, a Cornell University scientist.

Sojourner next turned toward Barnacle Bill, a 10-in.-high rock lying within arm's length of the lander, and closed in to sniff out its mineral content. Displaying a picture of the rover at the rock, the ever buoyant project scientist Matthew Golombek joked, "Here we have proof that Sojourner sort of nestled up and kissed Barnacle Bill." The high-tech buss, profferred by the rover's X-ray spectrometer, produced an unexpected finding: the rock was apparently loaded with silicon or silicon dioxide, commonly known as quartz.

What surprised many scientists was that the data appeared to liken Barnacle Bill to andesites, which are volcanic rocks usually found on Earth in the Andes Mountains and other areas of explosive volcanism. Andesites are typically formed by the repeated melting, solidifying and remelting that occurs during the tectonic-plate processes that shape and reshape terrestrial continents. Yet Mars seems to have very few volcanoes and shows no signs of tectonic plates, which suggested to some scientists that the planet wasn't internally active long enough to form andesites. Then what process could have created Barnacle Bill?

"How that happens in the absence of plate tectonics is not well understood," admits Robert Strom, a University of Arizona planetary scientist. To NASA Goddard scientist Jim Garvin, the finding suggests that a geology significantly more complex than scientists had expected was at work on Mars. "It's not the easiest rock to make," he says, "and that alone is very exciting."

Sojourner also managed to obtain a "fingerprint" of the other chemicals in Barnacle Bill. The fingerprint turned out to be virtually identical to those of the 12 meteorites found on Earth that are believed to have Martian origins. "So," concluded University of Tennessee scientist Hap McSween after the visit to Barnacle Bill, "now we can say that we have analyzed 13 Martian rocks."

Moving on, Sojourner headed toward a nearby, bear-shaped rock named Yogi, stopping on the way to test the consistency of the soil by using five of its wheels for traction and one to dig into the dirt. Sojourner's cameras showed that the rover's shove had displaced what seemed to be a thin layer of crust over the soil. "We used the rover as sort of a bulldozer," explained Golombek.

Then, demonstrating a technique that any driver maneuvering into a tight parking spot would envy, Sojourner energetically swiveled its wheels back and forth and "crabbed" sideways into a position near Yogi. The next day, however, when the rover moved toward the rock to perform X-ray spectroscopy, says project scientist Justin Maki, "it got a little too enthusiastic." What really happened is that Sojourner's controllers at NASA's Jet Propulsion Laboratory failed to take into account a small outcropping at the base of the rock. Pushed ever so slightly upward, the rover gently bumped into the rock and began trying to climb it. As one of the rover wheels began rolling up the side of Yogi, sensors aboard Sojourner detected a tilt and shut down the little vehicle, leaving it hung up, in effect, on the rock.

A low groan swept across the operations room at the J.P.L., and pictures transmitted by the lander soon afterward showed Sojourner askew, leaning against Yogi and seemingly helpless. But a quick check of the rover's systems confirmed that it was in good health, and controllers had little doubt that they could restart Sojourner, back it off the rock and try a better approach.

No such luck. On Sol 6, NASA's designation for Pathfinder's sixth day on Mars, they transmitted the appropriate instructions to the lander, which was to relay them to Sojourner. But the Pathfinder team had inexplicably failed to awaken the lander, which is shut down every Martian night, and the message was not received. "One miscalculation cost us the whole evening," sighed J.P.L. deputy project manager Brian Muirhead. As a result, Sojourner remained incapacitated and unable to operate the next day. That led a rover team member to crack, "On the seventh day, it decided to rest."

NASA has ambitious plans for Sojourner this week. It wants the rover to investigate Scooby Doo and Casper, two rocks that look intriguingly white in lander photos and just might contain hints of ancient Martian life. How so? To scientists, the duo's whitish hues suggest that they may be sedimentary rocks. "That would be awesome," says Ken Edgett, an Arizona State University geologist, "because sedimentary rock is the kind of thing that forms under water. And when you have water that sits around for a long time and sediments pour into it, the possibility of preserving fossils goes up."

Pathfinder's lander too should have a busy week. It is scheduled to shoot pictures of the Martian sunrise and sunset, the moons Deimos and Phobos and other features of the landscape.

Still, J.P.L. engineer Randii Wessen has some concerns. "We're living on borrowed time," he says. Sojourner has a 100% chance of surviving for seven days, he explains, "because that's what we designed it for. But after that, maybe it's got a 90% chance for eight days or 75% for two weeks." While the rover's electronics are protected in a warm box, the Martian temperatures, swinging wildly from 8[degrees]F to 130[degrees]F, may degrade the batteries. "We'll have to see how well they hold charges," says Wessen. Another threat, both to the lander--which is designed to survive for 30 days--and to the rover is Martian dust, which could coat the solar panels, affecting their ability to provide recharging current.

Yet at week's end the lander batteries were recharging smartly, and Pathfinder mission manager Richard Cook seemed unconcerned about Sojourner's fast-expiring design life. "I think at this point we're all expecting it to live for a long time," he said. "It has proved to be very capable."

And Cook was proved right. On the morning of Sol 8, Sojourner awoke, received its instructions and, after one more brief glitch, backed off Yogi, approached again and began eagerly sniffing out the rock's chemistry. Back at J.P.L., the exuberant Pathfinder team was predicting that Sojourner might live for weeks--and even months. Indeed, the little rover just could.

--Reported by Dan Cray/Pasadena and Dick Thompson/Washington

With reporting by DAN CRAY/PASADENA AND DICK THOMPSON/WASHINGTON