Hardy critters.
Electron microscope images of one-celled organisms called halophiles (left) and methanogens (right), which scientists think are tough enough to survive on present-day Mars.

Maryland Astrobiology Consortium, NASA and STScI

Life on Mars Remains Possible

Don't give up on the idea of martian life. A new study finds that some Earth microbes can survive and reproduce at the subfreezing temperatures that typify the Red Planet. Another report concludes that the chemical analysis carried out by the Mars Viking landers in 1976 may not have been sensitive enough to pick up signs of living organisms.

Reporting last Friday on the International Journal of Astrobiology Web site, a team led by astronomer Neill Reid of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, tested the coldest temperature limits for one-celled organisms--called halophiles and methanogens--which were collected from Antarctic lakes. The microbes belong to a group known as extremophiles, because they live in conditions that would kill most other forms of life on Earth. Indeed, when the researchers grew the organisms in a brine culture at minus 28 degrees Celsius, the microbes did just fine. The conditions are comparable to those of some martian subsurface environments.

"This was a striking result," says team member Shiladitya DasSarma of the University of Maryland's Center of Marine Biotechnology, also in Baltimore. He suspects that the organisms coped with the challenging environment by forming cellular aggregates: clumps of microbes that fight severe environmental conditions by sharing nutrients. This is the first time scientists have detected this phenomenon in extremophiles, he says.

The second potential boost for martian life involves a new chemical analysis of soil from harsh terrestrial environments on Earth. The twin Viking missions found no evidence of biological activity on Mars, but the principal evidence came from a process called the TV-GC-MS assay: Instruments aboard the landers rapidly heated the soil to vaporize its contents into small molecules for spectrographic analysis, which can identify the key chemicals involved in biology. Before the landers left Earth, NASA tested their instruments on Mars-like soils in places like Antarctica's dry valleys and the Atacama Desert in Chile. Although bacteria do exist in these soils, the assay couldn't pick up any signs of them.

A team from the National Autonomous University of Mexico in Mexico City decided to reanalyze those samples using more sensitive instruments. Biochemist Rafael Navarro-González and his team found trace amounts of organic matter in many of the samples, they report in this week's Proceedings of the National Academy of Sciences.

Despite the results, astrobiologist Bruce Jakosky of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, remains cautious. Even if the temperatures observed by the STScI team are the lowest seen for microbe activity, he says, the critical factor for martian life would still be liquid water--something not yet confirmed by NASA spacecraft. And as far as the study questioning the Viking results, Jakosky says that even a tiny bit of active biology should leave behind enough organic waste and dead organisms for Viking to detect. "If there are organics present that weren't detectable, it seems unlikely that they could have come from active biological activity," Jakosky says.

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