Clues to life on Mars may be hiding in one of the most inhospitable places on Earth, and a model Mars rover driving around there just found something interesting.
The Atacama Desert is a sort of nexus of science research. The desert in Chile is dry as a bone, receiving less than an inch of rain per year, and a lot of astronomical observatories live out there because of the dry air. The Atacama is ideal for another kind of space research, too. Those dry, arid conditions are just about as close as you can get to Mars here on Earth.
"Some of the most Mars-like soils on Earth are in the Atacama Desert in Chile," says Stephen Brian Pointing, a professor at the Yale-National University of Singapore. "There is very little water input to the desert and soils have become very nutrient-poor and extremely salty and alkaline over time, and this is very similar to the way that Martian soils have developed."
As a result, life doesn't exactly thrive here. But as Pointing and his colleagues point out in a paper today in , life does survive, which could point the way toward finding what modern day life persists on Mars, if any.
Pointing and his colleagues looked for life by building their own little Mars rover. The bot dug under the salty, dry soil of the Atacama, and often came up empty. He says the air and top soil had an average number of bacteria, but down below was usually more barren in terms of life. And yet the rover found little pockets along the way where extreme, brine-loving microbes thrived, make those micro-residents some of the hardiest organisms on Earth.
"Just below the surface is where it starts to get interesting," Pointing says. "We saw that with increasing depth the bacterial community became dominated by bacteria that can thrive in the extremely salty and alkaline soils."
Pointing says the finding also demonstrates that wherever life could exist in the Atacama, it did. "Overall the bacterial distribution in soil horizons was also extremely patchy and this was correlated with increased salt levels that limited the bio-availability of water," he says. "These bacteria clearly survive right at the limit of habitability."
Now let's take that to Mars, a once-wet world whose water is now isolated into brine, it's surface battered by radiation and some of the driest conditions in the solar system. According to the paper, we might still be able to find isolated pockets of life there by looking at the very limits of habitability in the subsurface environment.
There are a few problems, Pointing says. One of which has to do with the relative rarity, and the other of which deals with the actual conditions the life might be under.
"The patchy nature of the colonization suggest that a rover would be faced with a 'needle in a hay stack' scenario in the search for Martian bacteria," he says, wherein a rover has to look over and over, hoping to get the right spot. "Also, our study showed that paleo-soil features formed long ago when water was abundant but with no recent history of water input had no recoverable bacteria, and Martian soils are likely very similar to these in many places."
So it might be hard for life to persist on Mars today, but not impossible—and if we need any place that's a proof of concept, there's a desert in South America ready to provide us some hints.