In a darkened basement room in Oakland last week, about a dozen scientists sat staring intently at the projected image of a gray rock.

	Martha Rial, Post-Gazette Planetary geologist Nathalie A. Cabrol, right, and Italian geologist Gian Gabriele Ori participate in the daily meeting at Carnegie Mellon University to discuss Zoe's efforts in the Atacama Desert. Click photo for larger image. Related article CMU-developed computer interface aids in planning

They were searching for life.

At this point in a story, it is customary to make a qualifying statement, such as "but this was no ordinary gray rock." Yet it seems that this smooth stone, photographed last week by a robot out in the middle of Chile's Atacama Desert, really was pretty ordinary.

Its ordinariness only seemed to add to the intrigue for these scientists. They are part of a NASA project to search for life in the Atacama, one of the driest places on the Earth and an environment with some similarities to Mars.

With the image of the pebble-size stone blown up to about a foot in diameter on the projection screen, Shmuel Weinstein, a research biologist at Carnegie Mellon University's Molecular Biosensors and Imaging Center, pointed out several whitish veins ---- likely quartz ---- in its center.

Then the image was switched to a fluorescent view of the same rock, showing a fluorescent dye that binds to protein. Bright spots that traced the whitish veins were visible in this second image.

Was this evidence of some life form? If so, why was it only in the whitish areas? Had the dye detected an endolithic microbe ---- one that lives inside rocks? Or was this rock really as lifeless as it looked in natural light, with the protein dye binding to the mineral for some fluky reason?

"If it was mineral fluorescence, you'd think you'd see it over the whole rock, or in the veins," observed Nathalie Cabrol, a planetary scientist at NASA's Ames Research Center in California and the lead scientist for the Life in the Atacama project. "But it's spotty."

And then it was time to move on, as the team looked at other rocks and other suspicious fluorescent signals and continued to try to make sense of the information being transmitted from Carnegie Mellon's Zoe robot, some 4,400 miles away.

This is the second year ---- and the second field test ---- for the Life in the Atacama project, which is developing technology and methods that might eventually be used to remotely search for life on Mars.

Just as Mars appears to have once had surface water, the Atacama had lots of water during the last Ice Age, Cabrol said. It now is one of the driest places on Earth, with annual precipitation measured in millimeters. In many parts of the desert, it is hard to find any sign of life.

The project hopes to determine whether it is possible to unambiguously find signs of life in an area where life, if it exists at all, is known to be sparse.

Since August, one group of researchers has been in the desert, tending to the four-wheeled, solar-powered Zoe and her on-board sensors. Another group, a science team of biologists and geologists from NASA, Carnegie Mellon and the universities of Arizona, Iowa and Tennessee, has worked primarily from Pittsburgh.

During two week-long "traverses," one in September and one last week, the project has operated much as an extraterrestrial search for life might proceed.

The science team in Pittsburgh, using satellite photos and panoramic video images from Zoe, decides what areas they would like to explore and sends instructions each night to the robot. Zoe follows those directions the next day, gathers images along traverses that can cover several kilometers, and then transmits the data to Pittsburgh at the end of the day.

One of Zoe's primary instruments is a fluorescent imager developed at CMU's biosensor center and mounted underneath 9-foot-long, 6-foot-wide vehicle.

To generate an image, the device first sprays some water on the area of ground to be studied, with the hope that water might revive any dessicated life forms and make them easier to spot. The imager then sprays a succession of fluorescent dyes ---- one that binds to chlorophyll, one to protein, one to DNA ---- and snaps an ultraviolet image of each.

Last month's traverse was in a coastal area of the desert, where the team might expect to find life. Several sites showed signals consistent with life, Cabrol said.

"But some of the signals were pretty weird," she added, causing the team to wonder if the dyes were penetrating sufficiently. It's possible, they reasoned, that whatever bug or other life form could survive in such a dry place might have unusually hard shells.

But then Carnegie Mellon's Lauren Ernst, project chemist, had an idea: Instead of spraying the specimens with plain water, why not add a little acid, in the form of vinegar, to help dissolve minerals? After testing the vinegar solution on rocks in the CMU lab, the team decided to use the solution during last week's traverse.

	Carnegie Mellon University Zoe in the Atacama. Click photo for larger image.

"I personally believed this would be a pretty quiet week," Cabrol said, explaining that Zoe was in one of the driest, most barren parts of the desert last week. But it was quite the opposite. "We're seeing positives and lots of them."

The change was so notable that the scientists weren't sure if what they were seeing were true signs of protein and other organic molecules or some problem with their method.

"For a long time, people have been looking at the Atacama and not seeing any [living] thing," Cabrol said. "Now, [the images] are lighting up like Christmas trees.

"This is really exciting. We still don't know what to make of it."

The desert team is collecting all of the rocks and soil that Zoe is surveying, so the scientists will eventually be able to compare what they've seen on the transmitted images to the actual specimens.

In addition to adjusting their imaging methods, the science team also is refining its search strategy.

"When you're a geologist in the field, you want to cover lots of ground," Cabrol said. Covering lots of ground would seem to increase the chances of finding of life, she added. So, in contrast to the Mars Exploration Rovers now exploring the geology and hydrology of the Red Planet, Zoe is designed to cover several kilometers a day.

But the scientists more than once have pondered whether it was worth returning to promising sites to snoop around a bit more. "By going long distances, are you increasing your chances of finding life, or of missing it?" Cabrol wondered. In the future, mission planning may include more allowances for these second looks, she suggested.

And, perhaps by next year's field test in the Atacama, Zoe may be given more on-board intelligence and more freedom to stop and investigate promising areas she happens upon. It may be possible to program the robot with "a library of priorities," for making these spur-of-the-moment decisions.

"She's a pretty smart gal already," Cabrol said of Zoe. "We want to make her bright."