The more scientists have learned about Mars in recent years, the more some believe that finding life might involve a deep drilling project.
With the surface of the red planet desolate and mostly dry, one consistently appealing idea has been that pockets of underground water might harbor microbes. The problem is, studies have suggested reaching the pockets might require drilling a thousand feet (hundreds of meters) below the surface.
P. Buford Price, a physics professor at the University of California, Berkeley, has an idea for another place to look. If there is any life in the belly of Mars, some of it might be found around meteor craters, where rock has been tossed up from deep down.
The idea fits with recent suggestions by European scientists that pockets of methane in Martian air could be signs of life below. Methane should not last more than 300 years in the atmosphere, so the concentrations of it suggest a source that might be biological, the Europeans reason.
On Earth, even in solid rock 660 feet (200 meters) below the surface, methanogens have been found to thrive. Methanogens are ancient relatives of bacteria that take in hydrogen and carbon dioxide and emit methane.
Price and his colleagues have found that the same creatures deep in Antarctic ice emit enough methane to affect concentrations of the gas detected in drilling projects. Methane pockets in ice cores taken from Greenland registered levels of the gas that in spots were 10 times higher than expected.
"We found methanogens at precisely those depths where excess methane had been found, and nowhere else," Price said.
Craters already dug
While Earth and Mars are very different places, and no one knows whether the source of the methane on Mars has anything to do with life (it could be geologic in nature) Price figures the whole thing can be tested out without the need to drill too far down.
Under Antarctic ice, his team was able to detect concentrations of methanogens as low as 16 per cubic inch.
"Detecting this concentration of microbes is within the ability of state-of-the-art instruments, if they could be flown to Mars and if the lander could drop down at a place where Mars orbiters have found the methane concentration highest," Price said. "There are oodles of craters on Mars from meteorites and small asteroids colliding with Mars and churning up material from a suitable depth, so if you looked around the rim of a crater and scooped up some dirt, you might find them if you land where the methane oozing out of the interior is highest."
The idea was published online earlier this month by the journal Proceedings of the National Academy of Sciences.