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CMU researchers heading to Chile to look for life on Mars

Monday, March 03, 2003

By Byron Spice, Post-Gazette Science Editor

One of the next steps in the search for life on Mars will be taken next month -- in northern Chile.

A solar-powered robot formerly known as Hyperion has been refitted by the Robotics Institute for field experiments next month in the Atacama Desert. David Wettergreen, technology leader of the team, says future field experiments will use a new robot. Online graphic: Robotic astrobiology.

Sure, NASA is set to launch its Mars Exploration Rover mission later this year. But when the mission's twin robots land on the Red Planet next January, they will be looking for geological clues to how water has shaped the planet, not for signs of life.

Searching for life -- or even extinct life -- will be a much tougher job. That's why researchers, including two teams from Carnegie Mellon University, are heading to some of the most desolate spots on Earth, where conditions mimic those of Mars, to develop and test new biological detection technologies and intelligent robots.

"Anywhere you go on Earth -- almost anywhere -- you find evidence of life," said David Wettergreen of CMU's Robotics Institute. But in the Atacama Desert of northern Chile, the world's driest desert, organic molecules are few and far between. "There are almost no spores in the Atacama, almost no bacteria."

Since two Viking spacecraft landed on Mars in 1975, scientists have known that, if life exists there at all, it must be sparse or deeply buried. So if they have any chance of finding Martian life, they'll first have to manage that feat in places like the Atacama.

Next month, researchers from two Carnegie Mellon teams -- the Robotics Institute and the Molecular Biosensor and Imaging Center -- will head to the Atacama for the first of three field expeditions. Both are being funded through NASA's Astrobiology Science and Technology for Exploring Planets program.

The robotics group, which last month received a $1.3 million, three-year grant, is developing a four-wheeled, solar-powered rover that not only will be able to navigate hundreds of miles autonomously, but will have enough smarts to identify areas most likely to harbor life. It will be able to flip over rocks or scrape the soil as necessary to find active or extinct life forms.

The biosensor group, with a three-year, $900,000 grant, is adapting fluorescent techniques that allow scientists to microscopically study the function of living cells in the laboratory for use in a system that can detect minute amounts of organic molecules on rocks or soil in the field. The instrument would be one of an array of instruments that a life-seeking robot might carry on Mars.

As part of the same NASA program, researchers from NASA's Ames Research Center and Spain's Center for Astrobiology are testing new drilling technology in a search for subsurface life along the Rio Tinto, a river in southern Spain with a pH similar to automobile battery acid. As daunting an environment as the Atacama, the soils of the Rio Tinto nevertheless harbor a surprising abundance of microbes.

The possibility of life on Mars has long been the subject of lively debate. Percival Lowell and other astronomers of the late 1800s and early 1900s had argued that channels visible on Mars through telescopes of the day indicated the existence of civilization, but that idea was derided even at that time by most of their colleagues. More recently, the so-called "Face on Mars" seen in images returned by the Viking Orbiter in 1976 sparked similar speculation, but a clearer picture made in 1998 by the Mars Global Surveyor orbiter showed it consisted of natural landforms.

Since 1996, scientists have argued whether a Martian meteorite found in Antarctica contains fossils of bacteria.

The two Viking landers, which analyzed soil samples in 1975, briefly appeared to have found evidence of life. In two experiments, soil samples were mixed with a nutrient broth, "sort of like dilute chicken soup," said Bruce Hapke, a University of Pittsburgh planetary scientist who was on the Viking science team. The idea was that living things would digest the nutrients, breaking them down and releasing certain metabolic gases.

It looked like some metabolic gases were released, Hapke said. But a third experiment that measured the mass of molecules in the sample -- a gas chromatograph mass spectrometer -- failed to find any molecules big and complex enough to be associated with life forms.

It soon became clear that the compounds released in the other two experiments weren't the products of metabolism, but were generated by "superoxides" in the Martian soil that tore organic molecules apart. The scant water vapor in the Martian atmosphere reacted photochemically with ultraviolet light to make hydrogen peroxide that permeated the soil, Hapke said.

"Nobody knew that at the time [the Viking experiments were designed] or we would have done something different," he added.

Like the Martian soil, the Atacama Desert has high levels of oxidants that readily destroy organic molecules, which may explain why it is so hard to even find spores there, despite the fact that winds routinely carry spores over the desert, said Wettergreen, the technology team leader for the robot project.

The detection method being developed by the CMU biosensor team would rely on fluorescent signatures of life. Many bacteria, for instance, carry chlorophyll, which naturally fluoresces, explained Alan Waggoner, director of the biosensor center. An instrument that can block out sunlight while illuminating a sample with lasers or other artificial light might be able to find such evidence on rocks and soil, he said.

The group also plans to use fluorescent dyes that are activated when they bind to certain types of molecules. One dye, for instance, fluoresces blue when bound to protein. Another shines orange when bound to DNA. Others fluoresce in different colors when attached to carbohydrate or lipids.

Any life form is likely to have some combination of those four types of molecules, Waggoner reasons. If the four dyes are sprayed on a sample, any spot that fluoresces in all four colors would be a candidate life form that would need to be microscopically examined more closely.

"Conceptually, it's very simple," Waggoner said, but it will require a lot of engineering to automate this laboratory technique and make it work in the field. In the first field tests next month, Waggoner will be taking a backpackable microscope -- still being designed and built -- to the Atacama to see if he can find evidence of life.

Nathalie Cabrol, a planetary geologist at the Ames Research Center in California, said a life-seeking robot would require an array of instruments to evaluate potential evidence of life -- stereo cameras, multispectral microscopes, mass spectrometers and environmental sensors for temperature, humidity and ultraviolet radiation.

"They will all be very complementary," said Cabrol, who is on the science team for the Mars Exploration Rover mission and is the lead scientist for the Robotics Institute's rover development program. "It would be surprising to find one [instrument] is better than another."

A life-seeking robot will need to be more than just pack mule for the instrument array, however. William "Red" Whittaker, the lead investigator for the Robotics Institute team, said the robot will need to recognize and seek out landforms or environmental conditions that are most conducive to life.

The Mars Exploration Rovers, which will each travel no more than a kilometer from the landing sites, have enough on-board intelligence to navigate themselves and avoid obstacles, but they will be supervised by humans who will assign them tasks. The robots envisioned by Whittaker, however, could traverse hundreds of kilometer and would operate without direct supervision, which will require them to make scientific judgments about where they should go.

An earlier CMU robot, called Nomad, demonstrated some of those qualities. Three years ago, Nomad picked out a meteorite in an Antarctic rock deposit known as Elephant Moraine. And, during a six-week, 130-mile Atacama trek in 1997, it found an unusual rock that turned out to contain a fossil.

Whittaker emphasizes that Nomad didn't recognize the Atacama rock as a fossil, but simply noted its shape and composition was different from the thousands of rocks surrounding it. Still, he added, "it actually was a very big thing" for a robot.

The four-wheeled robot that will go to the Atacama next month will be the machine formerly known as Hyperion. In 2001, it showed that it could navigate around Devon Island, located in Canada above the Arctic Circle, while always keeping its solar cell array pointed at the sun, which circles the island 24 hours a day during the summer.

At that high latitude, the 3-square-meter solar array was raised at a high angle to catch sunlight, much like a sail. For the Atacama experiments, which will occur along the Tropic of Capricorn, the array now lies flat on its deck.

Cabrol will be heading down to the Atacama this week to select a "landing area," a 60- by 20-kilometer area that contains detectable life. Using remote-sensing data of the area from space, the science team will then select a smaller landing site -- the same process used to select landing sites on Mars.

Wettergreen, the project's technology lead, said this year's experiments will focus on component testing and demonstrating that the robot can navigate 50 kilometers -- about 30 miles -- and keep its batteries charged.

A new robot will be designed and built for future field tests. By the final field test, in spring 2005, the robot should be able to carry a full array of instruments and operate autonomously for two months and 200 kilometers, he said.

The robot would follow a "traverse" leading from a relatively wet area where life can be readily detected into drier areas where no life has yet been found, Wettergreen said. Such a traverse would test the limits of the robot and its components for finding life and perhaps contribute to biologists' understanding of the Atacama.

"My sense is that the space exploration community will be experimenting in the Atacama for decades to come," Whittaker said.

Byron Spice can be reached at bspice@post-gazette.com or 412-263-1578.

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