Methane-producing microbes – the simplest and most ancient organisms on Earth - could survive the extremely thin air of Mars, say scientists, including one of Indian origin, who suggest that the findings may hold clues to finding life on the red planet.
The Martian surface is presently cold and dry, but there is plenty of evidence suggesting that rivers, lakes and seas covered the red planet billions of years ago. Since there is life virtually wherever there is liquid water on Earth, scientists suggest that life may have evolved on Mars when it was wet and life could be there even now.
"In all the environments we find here on Earth, there is some sort of microorganism in almost all of them," said Rebecca Mickol, from the University of Arkansas the US
"It's hard to believe there aren't other organisms out there on other planets or moons as well," said Mickol.
Previous research detected methane, the simplest organic molecule, in the Martian atmosphere. While there are abiotic ways to produce methane - such as volcanic activity - much of this colourless, odourless, flammable gas in Earth's atmosphere is produced by life, such as cattle digesting food.
"One of the exciting moments for me was the detection of methane in the Martian atmosphere," Mickol said.
"On Earth, most methane is produced biologically by past or present organisms. The same could possibly be true for Mars," she said.
On Earth, microbes known as methanogens produce methane. They are among the simplest and most ancient organisms on Earth.
These microorganisms are anaerobes, meaning they do not require oxygen. Instead they rely on hydrogen for energy and carbon dioxide is the main source of carbon atoms they use in creating organic molecules.
The fact that methanogens neither require oxygen nor photosynthesis means they could live just beneath the Martian surface, shielded from harsh levels of ultraviolet radiation on the red planet. This could make them ideal candidates for life on Mars.
To see if they might survive extremely thin air, researchers, including graduate student Navita Sinha, experimented with four species of methanogens Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, and Methanococcus maripaludis.
Their experiments involved growing the microbes in test tubes within liquids as a proxy for the fluids potentially flowing through underground Martian aquifers.
The microbes were fed hydrogen gas and the liquids were covered with cotton swabs, which in turn were covered with dirt simulating what might be found on the Martian surface. The insides of each test tube were then subjected to low pressures.
Researchers found that methanogens survived exposure of lengths varying from three to 21 days at pressures down to roughly six-thousandths of Earth's surface pressure.
The study was published in the journal Origins of Life and Evolution of Biospheres.
