Carnegie Mellon University photos One of the successes of the final round of field-testing for Zoe was that the robot was able to avoid ruinous tumbles down steep slopes. Click photo for larger image. More Coverage: Robot Zoe: A pace with a purpose

Roaming the dry vastness of Chile's Atacama Desert, a biologist stops and peers at the ground; something catches her eye. She sprays several solutions on the spot, examines it again and . . . there, she sees it.

Life. It may be microscopic, but it shows signs of life.

Which is more than can be said for the biologist, who has never drawn a breath or taken a sip of water. Named Zoe, she is a four-wheeled, solar-powered robot on a search-for-life mission for NASA.

During a field test last year in the Atacama, Zoe followed directions from a science team in Pittsburgh and became the first robot to remotely detect life. But in a just-completed field test in the same desert, the driest place on Earth, Zoe outdid herself, finding life on her own at a spot she selected.

"This is really the next step in terms of exploration," said Nathalie A. Cabrol, a planetary scientist at NASA's Ames Research Center in Moffett Field, Calif., and lead scientist for the Life in the Atacama project. The Carnegie Mellon University robot showed that it not only could be a mobile platform for instruments, but can use its own rudimentary reasoning to make scientific discoveries.

"We are extremely pleased," Dr. Cabrol said. "She really did it on her own this year."

This latest field test, the third and final of the three-year project, also demonstrated Zoe's ability to navigate by herself for long distances without a map or human guidance, said David Wettergreen, the Atacama project leader and a researcher at Carnegie Mellon's Robotics Institute.

Though a mishap while Zoe was being transported in Chile by truck broke her axles and rattled her instruments, field repairs enabled her to complete the mission, despite sometimes erratic performance. And she performed admirably when winds kicked up to 40 miles an hour -- with 55-mile-an-hour gusts -- despite a four-square-yard expanse of solar cells that researchers had feared might act like a wing when Zoe was on slopes.

"The robot did fine," Dr. Wettergreen said. "It turns out that Zoe is pretty hardy in the wind."

A close-up of Zoe. Click photo for larger image.

The Atacama project was sponsored through NASA's Astrobiology Science and Technology Experiment Program, which is developing technologies and techniques that machines could use to detect life on Mars or elsewhere.

No one is under the illusion that planetary explorers will find little green men; if life exists or existed on Mars, the assumption is that finding it will require a lot of looking and digging.

"You can't assume that the site where you land will contain life," Dr. Cabrol said. "Mobility is a science instrument." Robots capable of covering a lot of ground and evaluating sites without human supervision will likely be essential.

In the Atacama field tests, Zoe would be placed for a week at a time at various "landing sites" in the desert, which over vast stretches appears devoid of life. A science team, encamped at Carnegie Mellon and not aware of the exact location of the landing site, would use Zoe's instruments to explore the site, sending her to designated spots that they thought promising for finding life.

Her findings would be uplinked by satellite to Pittsburgh each day for evaluation by the science team and instructions for the next day's operations would then be transmitted back to Zoe.

Zoe's primary instrument was a fluorescent imager designed by Carnegie Mellon's Molecular Biosensor and Imaging Center.

The device would look for the natural fluorescence of chlorophyll-containing plants, such as lichens. It also carried four types of fluorescent dyes that could be sprayed on the ground and would seek out constituents of life -- DNA, protein, lipids and cholesterol.

Last year, using this approach, Zoe and the science team were able to find various types of lichens as well as bacteria. In most cases, they found that this life was in a dormant state, said Shmuel Weinstein, a research biologist at Carnegie Mellon. Simply spraying water on a site often was enough to awaken this life and, in the case of lichens, trigger fluorescence.

The same basic approach was used in this year's field test, though the researchers also added a "science on the fly" component. That is, in addition to exploring the sites designated by the science team, Zoe would make intermediate stops on her own, spray some water on a site and see what happens.

She also was programmed so that she could recognize those rocks that were more interesting to the science team than others.

If the initial results looked promising, Zoe could then decide to do further tests with the four dyes.

Zoe was successful in these efforts at all three of the sites visited this year. "That got me really excited," Dr. Cabrol said. "To see that the robot is capable, on its own, of bringing us data that is important to the objective of the mission -- this is a spectacular result."

Alan Waggoner, director of Carnegie Mellon's Molecular Biosensor and Imaging Center, will discuss the search for life in harsh environments tonight at Cafe Scientifique Pittsburgh, an informal science discussion group. The meeting, which is open to all, will be at 7 p.m. today at the Penn Brewery, Troy Hill.