Mars shows evidence of vast flood Pathfinder's photos put deluge's width at hundreds of miles; Scientists 'in hog heaven'; Ancient wet condition raises question: Did forms of life exist?


PASADENA, Calif. -- With each new color photograph from Mars Pathfinder, scientists are recognizing the awesome magnitude of a deluge that swept over much of the red planet billions of years ago, a catastrophe that perhaps only Noah could appreciate.

From the shapes and colors of the rocks, surface textures and undulating low ridges and valleys, scientists inferred yesterday that the plain of Ares Vallis, where the spacecraft landed, had been scoured by liquid waters. The tilt of rocks and tails of debris behind pebbles suggested that the flood came from the southwest. Crustal splotches indicate that puddles left by the flood slowly evaporated, leaving what appear to be salty residues.

Michael Malin, a geologist and head of Malin Space Science Systems in La Jolla, Calif., estimated that the deluge was hundreds of miles wide, hundreds of feet deep and flowed for thousands of miles. "This was huge," he said, "but we don't know where the water went."

One of the big mysteries of Mars, which scientists hope Pathfinder and subsequent missions will solve, concerns the planet's ancient environment. Its surface is bone dry now, although vast amounts of frozen water are thought to exist in the northern polar cap and beneath the surface as permafrost.

But surface erosion indicates that in the past there was an abundance of water. The questions are: when and where? And could those wetter conditions have supported some forms of Martian life?

The Ares Vallis site was chosen because pictures from previous missions showed that it was probably a flood plain scattered with rocks washed down from nearby ancient highlands.

Scientists think the highlands are 4.5 billion to 3.6 billion years old, which is the same period in which life emerged on Earth. The early evidence indicates that the most recent flood at the landing site occurred 1 billion to 3 billion years ago.

In any case, Matthew Golombek, the chief project scientist at the Jet Propulsion Laboratory in Pasadena, said: "We're fairly confident that there was water on Mars. The only question is, could early Mars have been warmer and wetter and could liquid water have remained on the surface for any time?"

While scientists studied the pictures, the roving vehicle Sojourner continued its reconnaissance of rocks and soil out from the lander. Geologists said they had not completed analysis of the rover's first measurements of the soil chemistry, conducted Sunday. Those findings are expected to be announced today.

After making those measurements at the base of the Mars lander, the six-wheel Sojourner, about 1 foot tall and 2 feet wide, turned left and crawled over to a small knobby rock called Barnacle Bill. The rock is only 8 to 10 inches long, a little shorter than the rover and about nine feet south of the landing craft.

Pictures transmitted early yesterday showed, as Golombek said, that Sojourner "nestled up and kissed affectionately Barnacle Bill."

Sojourner's principal scientific instrument is an alpha proton X-ray spectrometer, designed to bombard a rock with protons and record changes in them as they return to the instrument. In this way, the spectrometer should be able to determine any elements in a rock's minerals, except for hydrogen and helium. The results will be the first determination of the composition of Martian rocks.

Later in the day, Sojourner's solar-powered electric motors moved it to the right for a study of the texture of a sandy flat area. Its wheels dug into the soil to check its depth and firmness. Early indications are that the landing site is coated with a veneer of powdery soil, about like flour.

Tracks left by cleats on Sojourner's metal wheels show that the powder appears to clot into definite shapes, not because of moisture but perhaps from an electric charge in the thin air.

Then Sojourner prepared to take on its next target, a small dark bear of a rock called Yogi. The rock, about 3 feet long, is more than 15 feet from the lander. After a few more days in the lander's vicinity, scientists say, Sojourner will be sent on longer, more adventurous journeys.

Project officials continued to be pleased with the progress of the mission since Pathfinder landed on Mars on the Fourth of July.

"The spacecraft is operating perfectly, rover is operating perfectly, and all the instruments are operating perfectly," Golombek said at a news conference yesterday.

Project scientists showed new pictures taken after the mast holding Pathfinder's camera was raised to its full height of more than 5 feet. "What a change from yesterday," said Peter Smith of the University of Arizona, head of the photograph-interpretation team.

From the higher perspective, the two lenses of the camera could see the edge of a dry channel beyond a line of leaning rocks. Some of the nearby rocks turned out to be smaller than they had seemed in earlier pictures.

Malin, who has spent years studying the geology of catastrophic floods and volcanic eruptions on Earth, said, "I'm in hog heaven, looking at these pictures of Mars."

Among the first things he noticed, which had not been apparent in earlier pictures, were patterns of grooves in the landscape south of the Pathfinder lander. They were presumably caused by the flood's scouring and redeposition of rocks and soil.

The ridges are about 10 feet high and about 70 feet apart. Malin said these could provide clues to the depth and velocity of the flood waters flowing across the plain.

Another question regarding the flooding remains unanswered. Were the floods primarily rampaging water carrying some soil and rocks, like an overflowing Mississippi River? Or were they more like mud flows, about half water and half soil and rock? The latter, Malin said, could have transported greater amounts of huge boulders.

Pub Date: 7/08/97

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