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Penn State researchers contemplate existence of life on early Mars

Posted on: Wednesday, 5 March 2003, 06:00 CST

Penn State researchers contemplate existence of life on early Mars

Source: U-WIRE

UNIVERSITY PARK, Pa. -- As NASA prepares for the launch of two rovers to determine the history of water on Mars later this year, Pennsylvania State University researchers are working with the agency to explore whether the early atmosphere of Earth's neighbor was warm enough to support life.

The NASA Astrobiology Institute, of which Penn State is a leading member, includes 14 other universities and government labs, including the University of Colorado, Woods Hole Oceanographic Institute, the Jet Propulsion Laboratory and Harvard University. Astrobiology is the study of geology and biology of planetary bodies.

Penn State researchers are primarily focused on early geological and biological evolution on Earth. Other teams determine oxygen levels in the early atmosphere or use DNA sequences to construct evolutionary trees to look at evolution from a biological standpoint.

James Kasting, professor of geosciences and meteorology, said a fluvial, or river-like feature on Mars called Nanedi Vallis, is similar in size to the Grand Canyon and is also an indication that Mars was warm for extended periods of time.

"Features like this had to form over millions of years, and they required a considerably warmer climate to do that," he said.

Mars has only 10 percent the mass of our planet, so its interior could cool off quicker. At that point, it could no longer sustain volcanism or plate tectonics, preventing the recycling of carbon dioxide that makes Earth livable. The two planets are about the same age.

Satellite imagery shows fluvial features on the surface of Mars, which may indicate there was once running water there. The temperature on the planet today is too cold for liquid water, however. Scientists are now trying to figure out if this was always the case.

"We're trying to figure out how we can warm early Mars," said Hilary Justh [graduate-geosciences].

The temperature on Mars today usually falls between 218 and 225 degrees Kelvin. The freezing point of water is higher than that, at 273 degrees.

The fluvial features were formed more than 3.8 billion years ago. Back then, the sun's intensity was only 75 percent of what it is today, because the star was still developing. This is known as the "faint young sun problem."

Several alternative theories have attempted to explain how early Mars could have stayed warm. One involved carbon dioxide acting as a greenhouse gas, but this was eventually disproved. Another theory said carbon dioxide could have condensed into clouds that would insulate the planet. This would require a full layer of cloud cover surrounding the planet, however, which is unlikely.

Still, others believe Mars was not warm for extended periods of time. They theorize that Mars was only warmed temporarily after getting hit by asteroids.

Based on previous research, Justh and Kasting knew methane was an effective warmer in Earth's early atmosphere. They began running various combinations of carbon dioxide surface pressures and methane levels through a computer model of early Mars to determine the surface temperature. They determined that the peak temperature was 248.33 degrees Kelvin, which occurred when a specific combination of surface pressure and methane existed in the atmosphere. This was 41.51 degrees higher than the value without methane. Methane, however, increased the surface temperature only to a certain point; after that, it cooled the surface.

Mars currently has an undetectably low level of methane. Where the methane from its early development has gone is still unknown.

Today Mars is "a very cold, very inhospitable" place, Justh said. The researchers are now rerunning their computer models for early Earth to see why the results for early Mars produce an anti-greenhouse effect, a result that is not seen on early Earth.

There are two varieties of methane sources that might have produced levels necessary to warm the planet: biotic and abiotic. Biotic methane is formed by living organisms while abiotic methane is formed through other natural processes. The researchers have determined there were not enough abiotic sources on early Mars to raise the surface temperature to the maximum value found -- which may point to the possibility of simple organisms.

"Either we're missing some abiotic sources, or it's life," Justh said, adding that it is a very controversial issue.

Kasting has not reached a decision about whether the early martian surface supported living organisms such as bacteria.

"They might have been there, they might not have. If they were there, it is easier to understand how the surface could have been warm," he said.

The warm Mars theory worked on by Justh and Kasting remains a work in progress.

"We're building a case based on observation and computer models, but one sample from the surface of Mars could change our theory," Justh said.

Confirmation of the team's theory may have to wait until after 2020, when it is believed the first craft that will return to Earth with Mars rocks will be launched.

"Until we get sample return missions, it's unlikely to know the answer to the question of life on early Mars," Justh said. She said several interesting locations on Mars to return rocks from have already been identified.

"What caused Earth and Mars to go on different paths if they were once similar is a matter of further research. The martian climate evidently cooled over time, but we still do not know how warm it was originally," Justh said.

(C) 2002 Daily Collegian via U-WIRE

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