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A lot of people talk about the possibility of life on Mars. Steve Squyres is doing something about it. Squyres, a Cornell planetary geoscientist, is the leader of science teams for two upcoming missions to Mars.

"Finding evidence of life on Mars would radically change the way we think about life on our own planet," says Squyres. His voice lowers and he whispers, almost conspiratorially, "It would change everything."

Squyres' experiments, part of NASA's Mars Surveyor program, are called APEX and Athena. Each is designed in part to investigate whether life has ever existed on the red planet.

Mars "We have devised a strategy to tell us a lot about Mars, and at the same time that maximizes the chance of finding evidence of ancient life," says Squyres.

If there is any place beyond Earth where life seems likely to have taken root, it's Mars. With volcanoes indicating a once-active source of energy deep within the planet, and ancient valleys almost certainly carved by running water, Mars may have once looked much more like our own planet. Scientists wonder if Mars, like Earth, could also have served as an incubator for life.

"We know that life came into being on Earth. But no one understands how non-living turns into living. Yet it happened, and no one has been able to duplicate it," explains Squyres.

The geologic record of the earliest forms of life on Earth is gone. Even in some of the very oldest rocks on our planet, scientists have found complex microbial fossils, with forms too complex to have been the first living things on Earth. Erosion and melting of the Earth's crustal rocks have obliterated any record of "first life."

"On Mars, it isn't a problem to find rocks dating back nearly to the birth of the planet," says Squyres. Since Mars is so much smaller than Earth, it has cooled off more quickly, limiting the kind of large-scale rock recycling found on Earth. Plus, with a thinner atmosphere, Mars has experienced less erosion. According to Squyres, the oldest rocks on Mars should provide a "snapshot" of the early geologic history of the planet. If life ever did exist on Mars, Squyres believes that evidence of it could still lie hidden in a geologic record that's located more than 128 million miles away from home.

Lander 1 Site
View from Lander 1 Site. Big Joe, the large rock just left of center, is about 2 m (7 ft) wide. This rock may be a fragment of a lava flow that was later ejected by an impact crater. The red color of the rocks and soil is due to an abundance of oxidized iron in the eroded material.

The trick is getting that geologic record back to Earth for study. So far all the missions to Mars have performed experiments on rock samples located around the landing site.

"Doing that kind of experiment on Earth wouldn't necessarily yield signs of life either," comments Squyres. "There are many rocks on Earth that contain no fossils. What we need is to send a geologist to Mars to pick and choose rocks most likely to contain evidence of life. The Athena Rover is really a robotic field geologist."

The FIDO Rover, a prototype of the 2003 Athena Rover.

The 2001 APEX experiment and the 2003 Athena Rover will be the first steps in the quest to return rock samples from another planet.

NASA's 2001 and 2003 Mars missions will each put a lander on Mars, and each will carry a rover. The 2001 rover, known as Marie Curie, will stick close to the lander vehicle and help scientists decide which kinds of rocks they would like to study on Earth.

The 2003 Athena Rover, which will have a range of as much as 10 kilometers, will actually collect rock samples and place them into soccer-ball sized containers, which will in turn be blasted into orbit around Mars. The orbiting rock collections will be picked up and returned to Earth by a mission to be launched in 2005.

Scientists have long awaited extraterrestrial rocks to study. And Squyres is no different. Still, he is quick to issue a caution: "The probability of us coming back with fossils is probably slim."

If life ever existed on Mars, Steve Squyres is determined to find it. "When I was a kid, I was fascinated by exploration of all sorts. The deep sea, the polar regions. Captain Cook, and the other explorers. I originally went into geology to combine science and exploration. Going to Mars is the ultimate kind of science exploration -- because we just don't know what we're going to find."