PASADENA, Calif. -- Sojourner, the pint-size robot geologist, has taken the first chemical fingerprint of a rock on Mars and determined that it resembles the lava found on the Andes mountains.
Significantly, the 8-inch-high rock known as "Barnacle Bill" shows signs of repeated heating and melting, an indication that the red planet stayed warm longer than scientists previously thought.
This is another bit of evidence supporting the theory that Mars was once warm, wet and possibly hospitable to primitive life.
While the rover was practicing geology, its mother ship, Pathfinder, acted more like a tourist, snapping photos of a martian moon, Deimos, and a pale blue sunset.
The reddish dust scatters the red portion of the sun's rays, producing a bluish sunset -- the opposite of what happens on Earth.
The rover also executed what one scientist called "the first wheelie" on Mars, as it spun its aluminum wheels to test the composition of the soil.
By the end of its fourth working day yesterday, Pathfinder had sent 1,575 images to its home base at NASA's Jet Propulsion Laboratory in Pasadena. So far, about half of the scenes that make up the "monster pan" -- a full-color, 3-D panorama of the landing site in Ares Vallis -- have been processed.
But even the partial images displayed at a news conference yesterday -- and on the World Wide Web -- displayed a wondrous smorgasbord of rocks of various shapes and hues.
"This really is a rock festival," gloated Hap McSween, a geologist at the University of Tennessee who is attached to the Pathfinder mission.
McSween said Barnacle Bill was apparently swept down from the southern highlands of Mars in the enormous flood that occurred a billion or so years ago.
"This rock contains the fingerprints of Mars," he said.
About one-third of Barnacle Bill is composed of the same material as the martian meteorite that fell in Antarctica 13,000 years ago, and which some scientists believe contains the fossils of tiny organisms.
Another third of the rock is made of quartz and the rest of feldspar, two of the most common minerals on Earth.
The combination is like "andecite," a type of rock found in volcanic lava flows in the Andes. Mars, like Earth, has been a volcanic planet since its formation 4.5 billion years ago, McSween said.
The scientists determined the composition of Barnacle Bill by using a device known as an alpha proton X-ray spectrometer, part of the equipment on Sojourner. The spectrometer is an extremely sensitive device that can determine the elements in a sample by spraying it with radioactive protons and measuring the energy that bounces back.
The weather on Mars yesterday stayed about the same as the previous day: light winds out of the west, and temperatures ranging from 6 degrees above zero to 105 degrees below zero Fahrenheit.
"The weather on Mars this season is pretty boring," said Jeffrey jTC Barnes, an Oregon State University meteorologist attached to the Pathfinder mission. "It's the same day after day in the northern summer in subtropical Mars."
But Barnes predicted that the weather will change dramatically in a couple months, when the Martian autumn begins. At that time, the fine dust that fills the atmosphere up to about 25 miles will grow even thicker.
Pub Date: 7/09/97