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Juicy evidence hidden under Martian lava

Scientists say a mysterious lava flow has buried what they had hoped would be geological traces of ancient water at the Spirit landing site on Mars.
The cover of the journal Science features a portion of the "Mission Success" panorama acquired by the Spirit rover on Jan. 8. The view is to the east; the Columbia Hills in the distance are about 1.5 miles (2.5 kilometers) away and rise 325 to 650 feet (100 to 200 meters) in height.
The cover of the journal Science features a portion of the "Mission Success" panorama acquired by the Spirit rover on Jan. 8. The view is to the east; the Columbia Hills in the distance are about 1.5 miles (2.5 kilometers) away and rise 325 to 650 feet (100 to 200 meters) in height.Nasa / Jpl / Cornell / NASA / JPL / Cornell
/ Source: Reuters

A mysterious lava flow buried what Mars experts had hoped would be good evidence of a planet once covered with lakes and rivers, scientists said Thursday.

To add insult to injury, the area has spent millions of years being bombarded by meteorites and pockmarked with rocks thrown up by nearby impacts.

The first 90 days of the Spirit rover’s explorations are documented in a series of reports in Friday's issue of Science that show puzzling lava flows and evidence of ice ages that vaguely resemble those once seen on Earth.

Spirit and its twin on the opposite side of the planet, Opportunity, have moved on to more exciting formations, but scientists have learned they can trust many of their instincts about what they have seen on Mars.

Where did the water go?
Spirit landed in the 95-mile-wide (150-kilometer-wide) Gusev Crater on Jan. 3 and rolled through pockmarks and around boulders, collecting dust, drilling into rock and taking spectrometer measurements.

“Gusev Crater is a place that we believe surely must have had liquid water on it at some point,” said principal science investigator Steven Squyres. “When you see a hole in the ground with a major riverbed flowing into it, it doesn’t take a rocket scientist to figure out there was water in it at some time.”

To their great disappointment, Spirit has found little evidence of that water, instead finding that a thick layer of basalt and other volcanic rock flowed over much of the crater, burying the juiciest evidence. It is not clear where the lava would have flowed from.

“We landed with hopes that we might be able to identify water-laying sediments. Instead, the rocks we found were all layers of basalt,” said Squyres. “There are little craters all over the place. Lavas have covered this region of Gusev Crater and then they have been all busted up by impacts.”

Dirty snow
One intriguing finding was a varnishlike coating on the surface, said Raymond Arvidson of Washington University in St. Louis.

“The cement may be emplaced by thin films of water coming up and out,” Arvidson said in a telephone interview. “My idea was that it involved thin films of water kind of chemically corroding the surface of the rock. I personally think it was done under maybe a meter (3 feet) of dirty snow.”

That could happen if, as scientists believe, Mars changed its spinning axis and the equatorial regions tilted away from the sun. That has happened on Earth, said Arvidson — notably during the ice ages when glaciers crept down from the poles.

“On Mars, it produces meter-thick snow on the equator,” Arvidson said.

Onward and upward
Squyres said the golfcart-sized Spirit had moved on to bigger and better things — a range of hills nicknamed the Columbia Hills.

“The hills are made of different stuff. We are still working out what that rock is,” he said.

Winter is reaching its peak, and the dust-covered rover is hard-pressed to get the sunlight it needs to operate. Squyres said that this week it was seeking a space on a flat span of bedrock facing north to bask in the waning solar rays.

“We are going to park on it for about two weeks,” he said. “We are going to hit this rock with everything we have got. We are going to brush it, we are going to drill holes in it.”