Martian mysteries

By Diana Steele
News Office

As the Mars Pathfinder continues to probe the red planet with its Sojourner rover, University scientists are busy analyzing the rock and soil samples retrieved by the rover.

While Sojourner moves across the rugged Martian terrain, its "snout" -- the Alpha Proton X-ray Spectrometer, designed by University scientists Thanasis (Tom) Economou and Anthony Turkevich -- is placed up against Martian rocks and soil to analyze their chemical content. Six soil samples and seven rocks have been analyzed so far, and Economou said the results have been surprising.

"The soil samples are all about the same composition," said Economou, Senior Scientist in the Enrico Fermi Institute, "and they match pretty well the soil analyses obtained by Viking in 1976. But there is a surprisingly high amount of silica in some of the rocks. A second type of rock has less silica but high amounts of sulfur and phosphorus that we can't explain."

Robert Clayton, the Enrico Fermi Distinguished Service Professor in Chemistry and Geophysical Sciences, and an expert on Martian meteorites, said, "If either the phosphorus and/or the sulfur levels are as high as they say, they are outside the range of anything we know on Earth as volcanic rocks. These analyses suggest that there are rock types we hadn't even suspected were on Mars."

"That means Mars is a much more interesting planet, geologically, than we thought," said Economou.

Clayton added that none of the rocks so far match anything on Earth we believe to be Martian meteorites. Gases trapped in some of those rocks match the profile of the Martian atmosphere measured by Viking in the 1970s. "It is a puzzle," he said.

Economou added, "Some people are having second thoughts about whether the meteorites we've found on Earth actually came from Mars, but we have analyzed rocks only on one side of Mars and can't exclude the possibility that the meteorites simply came from another site on the planet."

Sojourner will continue its exploration of the Martian plain near the landing site at Ares Vallis for as long as it can withstand the severe conditions on Mars. "The rover was only built to withstand one week on Mars, and now its in its third month and we're still getting good data," said Economou. "And it looks like we'll be here for a long time."

Economou and his team are not only busy analyzing data, they are preparing proposals to build the instruments for subsequent NASA missions to Mars. A launch in 2001 may carry a new, improved version of the APXS to analyze samples that are retrieved. This is in preparation for a mission in 2005 which will actually retrieve and return samples to Earth. In 2002, a joint U.S.-Japanese mission will carry on board a "nano-rover" (Sojourner is classified as a "micro-rover"), only six inches in length. "We have to scale down the APXS to one-fifth its current size," Economou said.

With the success of the APXS on the Pathfinder mission, Economou will probably be busy for many years to come. "People joke that I have a dynasty," he said, laughing. He said he is grooming his grandsons, 8 and 5 years old and students at the Lab Schools, to become Mars explorers, too, and take over the family business. "Every day I bring them down to the Lab Schools and I tell them what's happening on Mars today."