A team led by Vladimir Krasnopolsky of Catholic University has analyzed the existence of methane in the Martian atmosphere and found strong evidence bacterial action is the only plausible source of the gas. The planet's fabled little green men might be little green algae, alive somewhere under the surface - today.

I think it's a product of metabolism of methanogenic bacteria on Mars, Krasnopolsky, an atmospheric scientist, told United Press International. They catalyze carbon dioxide and hydrogen to form methane and water.

The team used a spectroscope on the Canada-France-Hawaii telescope at the Mauna Kea Observatory in Hawaii to detect a tiny proportion of methane - about 10 parts per billion - in the planet's atmosphere. They chose the instrument, Krasnopolsky said, because it has the highest available resolution to detect trace compounds such as methane on Mars and other neighboring planets.

A 10-ppb concentration might not seem like much, but it speaks volumes to scientists, because methane generally is not a long-lived substance in the atmosphere, particularly in trace amounts. It is transient. On Mars, methane would disappear within 400 years if something on or below the surface was not replenishing it.

For that source there are only two possibilities; one is volcanic activity. Methane can be produced from water and CO2, but only at temperatures higher than 2,200 degrees Fahrenheit (1,200 degrees Celsius).

The problem is none of the probes sent to the red planet - including the European Mars Express and NASA Mars Odyssey orbiters, and the twin Mars rovers, Spirit and Opportunity - have detected the slightest amount of volcanic activity. In fact, volcanism on Mars probably has been inactive for at least 10 million years.

The methane must be coming from bacterial action, Krasnopolsky said. We're pretty confident, he added.

The research is available online and will be published in the November issue of the journal Icarus.

Krasnopolsky has even calculated the concentration of microbes necessary to produce the amount of methane being detected in the Martian atmosphere. Assuming the biochemistry is similar to Earth-based organisms, he estimates there could be about 20 tons of methanogenic bacteria currently living on Mars - or, more precisely, under the surface.

That is a paltry amount compared to the tens of billions of tons of bacteria estimated to inhabit Earth. Krasnopolsky figures that each Martian bacterium, if evenly distributed across the planet, would have several square inches of real estate to occupy.

Bacteria tend to clump closely together in colonies, so on Mars they must be confined to just a few, isolated enclaves. That might be the reason why none of the Mars landers - the twin rovers currently operating, plus Pathfinder and its Sojourner rover in 1997, and the twin Viking landers in 1976 - has found any trace of alien bacteria.

So the next step in the search for Martian life is to isolate the source or sources of the methane. That might be difficult because the gas dissipates into the atmosphere so quickly.

However, just this week, an Italian physicist presented research that might lead to the most likely candidates for Martian bacterial colonies.

Vittorio Formisano, of the Institute of Physics and Interplanetary Space, Monday said he used data from the Mars Express to analyze gas emissions from Mars. He said the orbiter's instruments had detected concentrated patches of both methane and water vapor emanating from three locations - areas called Arabia Terra, Elysium Planum and Arcadia-Memnonia.

It turns out the three areas all suggest they harbor water ice just below the surface, which might constitute a haven for bacteria that can exist at extreme temperatures, such as those living under surface rocks in the desert areas of Antarctica.

Since last year, Michael Mumma, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., has been looking for methane on Mars using his agency's Infrared Telescope Facility at Mauna Kea, as well as other instruments in Chile and California. Mumma and his team have found the gas not only in concentrations up to 30 ppb, but also varying in concentrations according to location.

It certainly identifies key regions for further investigation on Mars, he said.

Although Mumma - chief of Goddard's planetary and astrophysical sciences laboratory for extraterrestrial physics - has said he remains cautious about the possibility of life on Mars, he also acknowledges it is not impossible that bacteria are living there.

Below the permafrost, he told the British journal Nature recently, there may be active regions of life releasing methane right now.

Other researchers have found organisms living more than a quarter-mile below the Canadian permafrost, for example, he said.

Mumma has proposed that NASA launch a space-based infrared telescope to hunt for heat sources on the Martian surface. The spacecraft, which could be launched as early as 2010, would observe Mars from a high Earth orbit - about 900,000 miles (1.5 million kilometers) away.

The proof of biological action, he said, would be the absence of other hydrocarbons in the atmosphere - such as ethane - that also are the byproducts of geological processes. If those compounds are absent, the finding would strengthen the case for Martian microbes - and the biggest discovery since Columbus set foot in the New World.

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