If the prospects of life on Mars were a pendulum, it's just swung back toward "favorable." An international team of researchers led by Washington State University planetary scientist Dirk Schulze-Makuch has found that the most Mars-like, apparently lifeless spot on the face of the Earth isn't so lifeless after all. Areas of the hyperarid Atacama Desert once thought lacking even microbes is showing blooms of specialized bacteria after rainfall, providing hope that similar dormant colonies may exist on the Red Planet.

The Atacama Desert is about as close to Mars as you can get on Earth. The Chilean desert has areas that are so inhospitable to life that not even bacteria can survive under normal circumstances. The nitrates falling from the sky that bacteria would normally gobble up remain uneaten and rainfall is measured in millimeters per decade. Though the 10 million-year-old desert is surprisingly cool with a Mediterranean climate, there isn't enough water to sustain life. Worse, the cooler temperatures means there's less energy available for growth and reproduction.

According to Schulze-Makuch, when the Washington study began in 2015, this reputation for utter lifelessness seemed intact. Though some microbes and traces of DNA have been found in the Atacama, these were always dying remnants that were unlucky enough to be blown in from the outside world.

That changed when the desert was subjected to its first rainfall in decades, activating long-dormant colonies buried under the surface that reproduced in that typically frantic manner of desert life making the most of the brief opportunity. When the team returned in 2016 and 2017, they found that the colonies had gradually gone dormant again as the soil dried out. However, by using sterilized spoons and special instruments, they were able to take uncontaminated samples and could identify several indigenous species of microbial life by genomic analysis.

"In the past researchers have found dying organisms near the surface and remnants of DNA but this is really the first time that anyone has been able to identify a persistent form of life living in the soil of the Atacama Desert," says Schulze-Makuch. "We believe these microbial communities can lay dormant for hundreds or even thousands of years in conditions very similar to what you would find on a planet like Mars and then come back to life when it rains."

Schulze-Makuch says that the implications for Mars are considerable. Though the Martian environment of today is so inhospitable that it makes the Atacama Desert look like Kew Garden on a spring afternoon, it was a very different place billions of years ago, with shallow seas, rivers, and lakes where very simple life could have evolved. It's possible that as the planet grew colder and drier, some lifeforms could have adapted by developing long-term dormancy.

"We know there is water frozen in the Martian soil and recent research strongly suggests nightly snowfalls and other increased moisture events near the surface," says Schulze-Makuch. "If life ever evolved on Mars, our research suggests it could have found a subsurface niche beneath today's severely hyper-arid surface."

The Washington team is scheduled to return to the Atacama Desert on March 15 for another fortnight's investigation, which will involve hunting for more microbes. In addition, the hope is to later study the Don Juan Pond in Antarctica, which is a very shallow lake so salty that it is liquid even at temperatures of -58° F (- 50° C).

"There are only a few places left on Earth to go looking for new lifeforms that survive in the kind of environments you would find on Mars," says Schulze-Makuch. "Our goal is to understand how they are able to do it so we will know what to look for on the Martian surface."

The research was published in the Proceedings of the National Academy of Sciences.

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