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Researchers suggest new place to look for microbial life on Mars: ice with bits of dust

Could microbes endure just beneath the surface of Mars, in layers of dusty ice exposed to just the right amount of sunlight? A newly published study suggests those might be among the most accessible places to search for signs of life on the Red Planet.

The study, published today in Nature Communications Earth & Environment, is based on models developed using impure ice from Greenland.

“We did not find any direct evidence for any microbes on Mars,” study lead author Aditya Khuller told GeekWire in an email. “We do find that the depths where the radiation (solar and UV) conditions are favorable for photosynthesis within dusty Martian ice intersect with the depths where dusty ice can melt on Mars.”

Khuller is a researcher at NASA’s Jet Propulsion Laboratory who’s due to join the University of Washington’s Applied Physics Laboratory at the end of the month. The paper’s co-authors include one of Khuller’s mentors, UW professor emeritus Steve Warren, whom Khuller says is “the world’s expert in how radiation interacts with snow and ice.”

Modern-day Mars is a cold, dry world, bombarded with life-killing levels of ultraviolet radiation. But scientists say that the planet would have been far more hospitable to life in ancient times. They suggest there’s a chance that hardy organisms could still be hanging on deep down in subsurface havens.

How deep? And how much of a chance? Those are questions that Khuller, Warren and their colleagues sought to answer by modeling the composition of Mars’ ice.

“We used impure Greenland ice instead of typical terrestrial snow, because it is likely that the dusty ice on Mars has also become coarse-grained since it was deposited sometime over the last million years, during a series of Martian ice ages,” Khuller said. The research team also factored in the presumed composition of Mars’ red, iron-rich dust.

Their conclusion was that there could be a sweet spot in layers of Martian ice where the dust could filter out UV radiation, while letting enough sunlight through to thaw out a trickle of water and support photosynthesis. That probably wouldn’t happen at the Martian polar caps, but it could happen in warmer areas at mid-latitudes.

The ice would have to be exposed to the surface. Khuller said one of the likeliest places to look would be in “the dusty ice that can get exposed by the overlying dry material slumping down within some gullies” on Mars. Such gullies have been areas of interest for astrobiologists for decades.

So, how deep might the habitable zone go? That depends on how much dust is in the ice, the researchers say. If the dust content amounts to somewhere between 0.01% and 0.1%, the zone could range between 5 and 38 centimeters (2 to 15 inches) in depth. If the ice is cleaner than that, the zone would be more like 2.15 to 3.1 meters deep (7 to 10 feet deep).

NASA is working with its commercial and institutional partners — including Jeff Bezos’ Blue Origin space venture, based in Kent, Wash. — to develop a plan for bringing samples back from Mars for study on Earth. But there are currently no plans to target deposits of dusty ice.

“We do believe that the dusty ice exposed at the Martian mid-latitudes within gullies would be excellent targets for future missions to search for signs of life on Mars,” Khuller said. “We hope that our findings will encourage the development of future missions to these locations to search for any potential life on Mars.”

In addition to Khuller and Warren, the authors of the study published by Nature Communications Earth & Environment, “Potential for Photosynthesis on Mars Within Snow and Ice,” include Philip Christensen and Gary Clow.