The Atacama Desert of northern Chile may be the world's driest desert, but areas of it nevertheless teem with life. So why can't NASA scientists find life there?

	Carnegie Mellon University photo
	Alan Waggoner, director of Carnegie Mellon's Molecular Biosensor and Imaging Center, examines a sample of Atacama soil.

True, a NASA-funded team of scientists who participated in an Atacama field experiment in April found plenty. They were pestered by flies, marveled at the variety of lichens growing on and under rocks and watched as vultures circled over their heads, a sure indication that mice skittered nearby.

But counterparts at the space agency's Ames Research Center in Moffett Field, Calif., poring over photos and instrument data transmitted from the field scientists, never found anything they considered proof of life.

For this team of NASA and academic researchers, assigned to develop robotic technology for finding life on Mars, those results might seem unsettling. If they can't detect life known to exist 5,000 miles away in the Atacama, how could they hope to determine if life exists on an alien planet 35 million miles away?

The researchers, who gathered at Carnegie Mellon University last week for a three-day workshop, nevertheless were pleased to discover that what they were able to discern about the geology of the desert by remote sensing had closely matched what scientists on the ground observed.

The results were encouraging, considering this was the first field experiment in what will be a three-year project, said Nathalie Cabrol, a planetary scientist at Ames and lead scientist of the Life in the Atacama Project. William "Red" Whittaker of CMU's Robotics Institute is the project's principal investigator.

But a host of issues remain for the dozens of researchers who are building the robot and the life-sensing instruments, which must eventually mesh to become a machine capable of scientific exploration.

"If I see a bush in front of my rover, there's not too much to discuss," Cabrol said. But if life is sparse, more subtle or resembles nonliving features, how do researchers pick out the signature of life? What features might prove something is living? What combination of sensors is needed to detect that signature?

The next mission?

With two robotic rovers now hurtling toward Mars to search for signs of water, the development of life-sensing robots gains greater urgency in the planetary community. If the Mars Exploration Rovers are successful in their quest when they land on the Red Planet in January, the logical followup mission would be a search for life.

"Mars is a dynamic planet, a water-enriched planet," said James Dohm, a planetary geologist at the University of Arizona who has spent years mapping it. Growing evidence that it is geologically active, with subsurface magma, suggests that water may not only be present as ice, but also as groundwater. And the combination of magma and water greatly enhances the prospects for finding life, he contended.

But no one knows how to prove life exists by remote sensing. And, as this year's Atacama field experiment underscored, even the human eye can be tricked in extreme environments.

Searching along the edges of the Salar Grande, an evaporated salt lake, the researchers came across numerous rocks covered by lichens -- leaf-like, crusty or stalk-like organisms that are combinations of fungi and algae. But not everything was as it appeared, said Alan Waggoner, director of CMU's Molecular Biosensor and Imaging Center.

Some of the rocks appeared to be covered with bumpy, green lichens, he noted. But when field researchers scratched beneath the surface, they discovered salt. The life-like bumps were simply salt that, through evaporation, had effloresced to form puffy mounds. The green outer layer turned out to be oxidized copper, which at some point had blown on top of the salt and been incorporated into it.

		The Mars show It will be months before NASA's latest robotic explorers reach Mars, but earthbound observers can get what should be the best view of the Red Planet in about 60,000 years at the end of this month, when Earth and Mars pass within 35 million miles of each other. Mars, which takes 686 days to complete its slightly elliptical orbit around the sun, makes a close pass by Earth every couple of years and comes particularly close every 15-17 years. The last time Mars was nearly this close was in 1988. The bright red-orange planet already is easy to see in the southern sky, though it doesn't rise until late in the evening. But as the month wears on, Mars will grow increasingly larger and brighter, will rise higher in the sky and will be visible earlier each night. This will culminate on Aug. 27, when Mars will be at its closest point and should be visible about half an hour after sunset. For more information on this event, visit the Planetary Society's Web site: planetary.org/marswatch2003

Though life is plentiful around Salar Grande, it's not necessarily easy to find, Cabrol said. Life forms there are very specialized, adhering only to certain types of surfaces, or growing only on slopes with a certain orientation to the sun.

"You can have life all around -- and then it disappears one meter away," Cabrol said. "You might find it on one side of a gully, but not the other."

The field team took CMU's Hyperion robot, a solar-powered, four-wheeled vehicle designed to operate autonomously. Hyperion, which eventually will be re-named to avoid confusion with an instrument of the same name aboard NASA's Earth Observing-1 satellite, carried high-resolution video cameras. Other remote sensing technologies tested in April included a spectrometer for identifying materials based on the colors of visible and near-infrared light they reflect and a microscope designed to detect biological molecules.

Dohm and other scientists at Ames who studied the data gathered by these instruments found it difficult to decipher.

"I have never looked through a rover camera. I've never been near a rover," said Kimberly Warren-Rhodes, an ecological microbiologist at Ames, who was part of that analysis team. Though experienced in field studies in the Atacama and the deserts of China, she said she never felt as if the information she was receiving was as good as she would get in person.

Waggoner, who used a microscope to look for naturally fluorescent chorophyll in samples, said several images he made of specimens could be interpreted as signs of photosynthesis. But Warren-Rhodes said she wasn't convinced.

"None of the samples could be confirmed unambiguously for life forms," she said. "My gut says it might be something, but I can't prove it."

The instrument Waggoner and his CMU colleagues are designing for the mission will not only look for chorophyll fluorescence, but also would apply four special dyes that would attach to DNA, protein, carbohydrates or lipids in a sample, each dye fluorescing a different color. A sample that contained all four substances, he reasons, could arguably be considered living.

A system for using those dyes wasn't available for this first field experiment. In fact, the instrument Waggoner took to the desert had to be assembled at the last minute. Though designed to be carried in a backpack, the microscope and its batteries weighed 50 pounds and ultimately broke the backpack. So he set the microscope up in a tent and brought samples to the tent, rather than following the robot around.

Retooling the robot

Eventually, the instrument will be incorporated into the robot. Based on what was learned this spring, the robot also will be substantially rebuilt for the next field experiment in September 2004, said the David Wettergreen, a research scientist at the Robotics Institute.

Carnegie Mellon University photo
Carnegie Mellon's Hyperion robot roams the Atacama.

The robot will need a new drive train so it can climb hills, better tires for traction in sand, a new solar cell array to produce more power and more computing capability.

"Pretty much all we're left with is some aluminum tubes" in the frame, Wettergreen said.

But Hyperion, originally designed for a different experiment, exceeded its performance goals during the outing, traveling more than 12 miles autonomously. At one point, it was able to operate on its own for one kilometer -- about six-tenths of a mile. By the time the project is over, the hope is that the robot will routinely operate with only one human command for each kilometer it travels, Wettergreen said.

That would greatly increase the range of a Mars rover and increase its chances of finding life. The two MER robots now on their way to Mars, by contrast, will travel no more than 10 meters without human direction and will cover no more than 40 meters a day.

Finding the right mix of sensors and robotics to give life scientists what they need is an extended endeavor, requiring all of the team members not just to share information, but learn each other's technical lingo, Arizona's Dohm said. Ultimately, everything must work together in an integrated system.

"We must integrate our disciplines to produce a true science craft," he said.