PROBE ROCKS OUT ON MARS; ROVER'S SAMPLES PROVIDE CLUES TO PLANET'S HISTORY.

Byline: Tony Knight Daily News Staff Writer

Calling the cornucopia of boulders at the Mars Pathfinder landing site a ``rock festival,'' mission scientists said Tuesday that early data from the football-size rock known as Barnacle Bill may change their concept of how Mars was formed.

The composition of the rumply volcanic rock indicates that Mars may have been hotter for a longer period of time in its early evolution, forming its crust much like Earth through ages of volcanic eruptions.

However, a measurement of the soil at the landing site revealed iron, magnesium, sulfur and other elements in similar quantities to the soil samples from the two Viking landing sites.

``This is probably a chemical fingerprint of Mars,'' said geologist Hap McSween, a member of the science team from the University of Tennessee.

The rover Sojourner spent most of the day Monday with its primary sensor pressed up against the Barnacle Bill rock and found silicon, oxygen and magnesium - stuff similar to Earth rocks formed in repeated volcanic eruptions.

Data from the Viking landings in 1976 and from meteorites believed to have fallen to Earth after being ejected from Mars by cosmic collisions showed no sign of this quartz type of rock.

``We thought the Earth was a very unusual place,'' said McSween. ``Now we find that Mars too has a crust with a lot of quartz.''

As the Martian day began Tuesday at the landing site at 3:18 p.m. PDT, the rover was ordered to move over to the big boulder that scientists have dubbed Yogi, because of its bearlike shape.

On the way, little Sojourner was ordered to lock five of its six wheels and spin one to dig beneath the surface of the Martian soil. In doing so, it torqued one of its wheels off the surface, said geologist Matt Golombek, the chief project scientist.

``That resulted in, just for point of information, a wheelie, the first wheelie on Mars,'' Golombek said.

Of more historical importance, Golombek said, is the fact that scientists for the first time have a little roving field geologist on the Martian surface. The Viking landers had robotic scoops, but none ever captured a rock to analyze.

``We have never before gotten a chemical analysis of a rock on Mars,'' Golombek said.

``Viking was a fixed platform,'' he said. ``It was a geologist's nightmare. You could see all these rocks, but you couldn't go out and look at them.''

Based on the Barnacle Bill analysis, the scientists are postulating that Mars formed much like Earth, with repeated volcanic eruptions mixing and remixing the elements of the planetary crust.

That means Mars is more like Earth than the moon, where volcanic activity ceased after the initial primordial lava flows.

``These high-silica rocks on Mars is really just amazing,'' Golombek said. ``If Mars was more like the moon, you could never get a high-silica rock.''

They cautioned, however, that the rock also might have been formed through other processes including a ``melt'' caused by a massive meteor impact.

Regardless of the interpretation, this is primarily a geological mission, and the geologists are ecstatic about it.

``This site really is a rock festival,'' said McSween. ``To tell you the truth, I really was scared at the start of the mission because when the lander came to rest with the base down, I was thinking it would be a mudfest.''

The scientists continue to name rocks in the area, and are referring to them as their ``rock stars'' as they guide the Sojourner rover through the region returning an enormous stream of data - the equivalent of about 72 floppy discs per day.

A total of 1,575 images have been downloaded from Mars, but the imaging team, which has been working 16-hour days since the landing, has fallen behind in processing them for release.

Also, mission flight engineers are preparing data from the air-bag landing that will be presented later this week. But initial readings indicate the lander bounced across the boulder-strewn Martian landscape at least 16 times on its air-bag cushion before coming to rest.

Data from Yogi was to be downloaded today, then the rover was to be off toward a whitish rock the scientists have named Casper. Other rocks to be visited within a few meters of the lander include Flattop, Shark and Wedge, and a patch of sand they've named Scooby Doo.

Also expected today is the final data for what mission scientists are calling ``the monster pan'' - a full-color, 360-degree image of the landing site.

``We hope to have it up on the Web site so that you can spin the scene yourself,'' said imager team leader Peter Smith.

Other data presented Tuesday included a Martian weather report. The high was 5 degrees Fahrenheit with a low forecast of minus 105. Air quality was dusty, but clear enough to see for miles.

The scientists said the dusty air scatters and absorbs light. Astronomer Nicholas Thomas said it gets light at the landing site at 3:15 a.m. Mars time.

``I'm pleased to announce that the only astronomical observatory on Mars is open for business,'' Thomas said.

The Mars imager is not a good telescope, he said, but its 12 filters allow the analysis of the spectra of light coming form the tiny moons of Deimos and Phobos.

Mission scientists said they also would try to image Earth in the Martian night sky, although they acknowledged that such an image would have no scientific value.