University of Arkansas researchers showed that certain species of methane-producing bacteria can survive the conditions on Mars pretty easily. Considering this result, they find it "hard to believe" that simple life isn't present on some alien planets -- as long as it has access to liquid water.
Simple organisms called methanogens could survive in the harsh conditions close to the surface of Mars and in its deeper soils, recent research suggests. The conclusion is particularly exciting as methane -- a byproduct of these organisms' activity -- has been detected in the atmosphere of Mars. The gas is often closely linked to biological activity on Earth.
Living under pressure
Although dwarfed in output by Earth's biosphere, there are non-organic sources of this gas such as volcanic eruptions. So scientists don't yet know what to make of the methane on Mars. But its presence does lend weight to the theory that there is life on the red planet despite its rocky soil, thin atmosphere, and limited supply of liquid water. In these conditions, complex life doesn't stand a chance. Hardy, simple life, however, does.
"We consider methanogens ideal candidates for possible life on Mars because they are anaerobic, and non-photosynthetic, meaning that they could exist in the subsurface," said Rebecca Mickol, a Ph.D. candidate at the Arkansas Center for Space and Planetary Science. "Just a few millimeters of Martian regolith is enough to protect the organisms from the dangerous UV and cosmic radiation that hits the surface."
"Additionally, methane has been detected in the Martian atmosphere, via multiple space-based and ground-based sources, including the Martian rover, Curiosity. Although these findings are still controversial, the presence of methane on Mars is particularly exciting because most methane on Earth is biological in origin."
Last year, Mickol and her team tested how well four species of methanogens could survive in the low-pressure conditions of a subsurface liquid aquifer on Mars using the planetary simulator at the University's W.M. Keck Laboratory. The bugs performed unexpectedly well -- all four cultures survived the exposure between 3 to 21 days. Given how prolific life is back here on Earth, thriving in unbelievably hostile conditions, it's probable we'll find it in harsh conditions elsewhere in the universe, Mickol says.
"The prevalence of life on Earth, in all kinds of 'extreme' environments, and the fact that life arose fairly early on in Earth's history, makes it hard to believe there isn't some sort of microscopic life on the other planets and moons in our solar system," she said.
Pradeep Kumar, an assistant professor in the Physics Department, wanted to see how the methanogens could fare much deeper into Mars' crust. He and his team tested one methanogenic species that passed Mickol's tests, Methanothermobacter wolfeii, in a hydrostatic chamber kept at 55 degrees Celsius (131 Fahrenheit), and progressively pressurized up to 1,200 times the surface level, with pH levels varied from 4.96 to 9.13 (7.0 pH level is neutral; anything below that is acidic, and anything above is alkaline). The temperature was selected as it is the "optimal growth" interval for the species. A martian geophysical model suggests that this temperature should correspond to a depth of about 30km -- for which the team selected the pressure and pH values.
M. wolfeii survived through all pressure and pH levels. In an acidic environment, its growth rate actually increased with pressure. For neutral and alkaline conditions, growth rate initially increased with pressure, then dropped as it grew.
"Given the discovery of methane in Martian atmosphere, our study raises an exciting possibility of methanogenic archaea to be a viable organism that can survive and possibly thrive in the subsurface conditions of Mars," Kumar said.
It's not conclusive proof that life exists on Mars -- the only way to find out is to go there and dig around. But it does add to a growing body of research suggesting that even Earth-born life can survive in space. So the odds of finding alien life look better and better by the second.
The full paper "Survivability and growth kinetics of methanogenic archaea at various pHs and pressures: Implications for deep subsurface life on Mars" has been published in the journal Planetary and Space Science.