Microorganisms Grow At Low Pressures, Implying Possible Life On Mars

"Our goal is first to get the organisms to grow well, then systematically experiment with conditions found on Mars," said Kral. He and his team first grew test tube cultures of various methanogens in a Mars soil simulant called JSC Mars-1. Derived from altered volcanic ash, it approximates the composition, grain size, density, and magnetic properties of Martian soil.

The researchers exposed the cultures to an atmosphere that consisted only of hydrogen and carbon dioxide, the raw materials methanogens need to produce energy. They incubated the cultures at each methanogen's optimal growth temperature. Methanogens release methane as a waste product, so the researchers were able to measure their growth by analyzing the amount of methane produced.

After successfully growing three different methanogens on Mars soil simulant, Kral moved on to the next step -- simulating various Martian conditions in the Andromeda Chamber, a large stainless steel vacuum container donated to the University of Arkansas by the Jet Propulsion Laboratory in Pasadena, California.

The chamber, which was originally constructed for comet simulations, consists of an insulated compartment with heating and cooling elements. A sample container, approximately one meter on each side, can be lowered into the chamber, which contains various detection and monitoring instruments. The device is believed to be the largest such instrument dedicated to space simulation research on a North American university campus.

The researchers grew methanogenic cultures in bottles and froze them. They inverted the frozen cultures and placed them below the surface of the soil simulant in the sample container, lowering it into the chamber. After sealing and evacuating the chamber, they replaced the atmosphere inside with an equal mixture of hydrogen and carbon dioxide at 500 millibars (about half the Earth's atmospheric pressure). Finally, they raised the temperature of the chamber to 35 degrees Celsius to ensure that the cultures melted into the soil simulant. A gas chromatograph was used to analyze samples daily.

So far, the Andromeda Chamber studies indicate low levels of methane production. This means that the organisms are metabolizing under low pressures, a significant finding. Martian life would have to be able to survive at such pressures, since Mars' atmosphere is much less dense than Earth's.

"The Viking Missions that landed on Mars in 1976 gave no substantial evidence for life on the surface today," Kral says. "There were also no measurable organic compounds detected. This led most researchers to believe that if life existed there, it was a long time ago, and is extinct today."

But Kral's work with methanogens got a significant boost from the discovery earlier this year of large quantities of frozen water below the surface of Mars. "With the recent successful missions to Mars (Pathfinder, Global Surveyor, Odyssey), and especially the discovery that there is probably a vast ocean of frozen water below the surface, there is a greater possibility that life may exist below the surface today."

Kral doesn't want to rush to categorical conclusions about the implications of his research, but if methanogens can grow well under simulated Martian conditions, it might be possible to take the organisms to Mars if humans ever colonize the planet.

"Of course, there are many potential ethical and environmental problems with this," Kral points out. Since methane is a "greenhouse gas," one that traps heat near a planet's surface, methanogens could theoretically be used to raise Mars' surface temperature, eventually "terraforming" the planet so that it could support life. However, Kral thinks this might take too long to be effective--perhaps hundreds or thousands of years.

Martian surface conditions include low pressure, low temperature, very little water, and an atmosphere that contains large amounts of carbon dioxide with almost no oxygen. Assuming that hydrogen and some water are present under the surface, the basic requirements for methanogen growth are met on Mars. And even if hydrogen is not present, carbon monoxide is, and some methanogens can use this instead of hydrogen.

Subsurface life on Mars would not be able to produce energy through photosynthesis, but would need to use chemical energy through the oxidation of inorganic matter. Such organisms are called chemoautotrophs.

Methanogens are chemoautotrophs that consume hydrogen and carbon dioxide, producing methane as waste. Few terrestrial organisms could survive anything approaching harsh Martian conditions, but methanogens can flourish in some of Earth's most inhospitable environments, such as ocean floor vents and peat bogs.

Kral wants to continue his research by experimenting with a range of Mars-like conditions, thoroughly analyzing the effects of lower pressures and temperatures on methanogenic growth, and ultimately ascertaining the effects of radiation, which is much higher on Mars because of its thin atmosphere.

What is the probability of extraterrestrial life? In all likelihood, it's quite high. But whether or not life actually exists on Mars -- or did exist sometime in the past -- is a question that terrestrial research can answer only partially. Kral's work paves the way for future experiments with Mars-like conditions and may one day provide a basis for studying biology in a real-life Martian laboratory.