Squyres captivates D.C. audience with story of rovers' year on Mars

NASA's Mars Exploration Rover Spirit photographed this scene on the slope of "Husband Hill" during the rover's 369th martian day ("sol"), on Jan. 5. The rock at the center of the frame was informally named "Peace." Spirit subsequently inspected the rock with the tools on the rover's robotic arm.NASA/JPL/Cornell

By Sarah Davidson

A tireless Steve Squyres paced the stage at the annual meeting of the American Association for the Advancement of Science (AAAS) in Washington D.C. on Feb. 18 as he held his audience of scientists, media and students spellbound by his recounting of more than a year exploring the surface of Mars.

Presenting one of the five AAAS plenary lectures, Squyres captivated his audience with the latest pictures from the twin Mars rovers Spirit and Opportunity. Squyres, a Cornell Goldwin Smith Professor of Astronomy and the principal investigator for the NASA mission, led the overflow audience through the events and discoveries of what was intended to be a 90-day mission to Mars, but which, for Spirit, is now over 400 days.

Earlier that day he had given a Mars update to a large gathering of international media at a AAAS news briefing. Squyres reported that Spirit has found its most interesting rock yet, dubbed Peace. It is an exposure of bedrock on the slopes of Husband Hill in the Columbia Hills in the Gusev Crater, which the rover has been climbing for more than six months now. Peace contains more sulfate salt than any rock Spirit has so far examined and is probably the most interesting and important rock Spirit has examined, Squyres said.

Steve Squyres, a Goldwin Smith Professor of Astronomy, at the AAAS annual meeting in Washington, D.C. Michael J. Colella/AAAS

The layers in the rock are cemented together by a substantial quantity of magnesium-sulfate salt -- Epsom salts. The salt could have come from liquid water with magnesium sulfate salt dissolved in it, percolating through the rock, then evaporating and leaving the salt behind. Or it could have come from weathering by dilute sulfuric acid reacting with magnesium-rich minerals that were already in the rock. "Either case involves water," he said.

Both rovers, and the mission team operating them, are "showing signs of age," as Squyres put it. Spirit's solar panels are collecting a fine layer of dust, which has reduced energy levels, but the rover and its twin are doing well mechanically and are continuing to send home valuable data from Martian surface. The Squyres team, operating mainly out of Cornell's Space Sciences Building and the Jet Propulsion Laboratory in California, holds planning meetings up to six days a week.

Squyres told the plenary audience, "The purpose of the Mars mission was to look for evidence concerning whether or not Mars had conditions on its surface that would have been suitable for life by trying to find evidence in the geological record." He added, "In other words, we set out looking for sedimentary rocks -- a sure sign that there was once water on Mars."

At first, Spirit's data disappointed the Squyres team because the vehicle had landed in a vast sea of uninteresting volcanic rock in Gusev. "All the rocks here told the same story -- we landed on lava -- and there were no sedimentary rocks around Spirit's landing site," Squyres said.

But, he added, "The nice thing about landing a rover, is that if you don't like the neighborhood you are in, you can go somewhere else." Unfortunately, the next destination, Bonneville Crater, turned out to be no more than a disappointing mix of sand and lava.

"Now it was day 100 of our 90-day mission," Squyres said. "Off in the distance, 2.5 kilometers away from the landing site, loomed an impressive set of hills we named Columbia Hills." It was thought that the hills were too far away for a vehicle designed to travel only 600 meters in its entire lifetime.

But, said Squyres: "On day 100 of the mission, we had driven the 600 meters the rover was projected to endure. We faced an important decision: we could assume the vehicle really only had about 90 days and 600 kilometers of life in it and stay in Bonneville to get as much science out of it as possible, or we could trust the vehicle and hit the gas."

Taking the risky route paid off. As soon as Spirit reached the base of the Columbia Hills 56 days later, it appeared to cross a geological boundary, and it hasn't detected lava since.

As Spirit climbed up and onto a feature dubbed Husband Hill, Squyres' science team finally hit bedrock and discovered the rocks it had been waiting for. The rocks are finely layered like sandstone and composed of minerals held together by a sulfur-based salt that comprises as much as 20 percent of the rock. This, said Squyres, is a sure sign that water played a major role in altering the rocks.

Meanwhile, Squyres reported, Spirit's twin, Opportunity, continues to stumble upon interesting rocks that tell of the region's rich history of water. The rover is now heading south to a "significant landmark" called Vostok crater.