Mars's Peroxide Snow Would Kill Any Surface Life

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These sparks break water and carbon dioxide molecules in the atmosphere apart and allow them to recombine into bleachlike chemicals, including hydrogen peroxide, the scientists say.

So much hydrogen peroxide is formed, in fact, that it would fall to the ground as snow.

This explains a conundrum dating back to 1976, when the first Mars landers, Viking 1 and Viking 2, failed to find any trace of organic matter in the Martian soil.

Hydrogen peroxide is a potent oxidant and antiseptic that rapidly destroys living matter. The old Viking result was surprising, says the lead author of the second study, Sushil Atreya.

That's because, even if Mars never had life, its soil should have contained substantial amounts of organic matter—certain types of carbon compounds that can be created through life-creating processes or geological processes.

"Organic material has been raining down from meteorites and comets for four and a half billion years," said Atreya, who is director of the Planetary Science Laboratory and professor at the University of Michigan.

"So where is it? This has been a big puzzle for 30 years. Something must be oxidizing the organic material" and thereby destroying it, he said.

Peroxide isn't a new culprit, but until now the only known Martian mechanism for creating it was decomposition of the atmosphere by ultraviolet light from the sun. That doesn't produce enough hydrogen peroxide to oxidize all organic matter in the soil.

Dust devils, on the other hand, can produce hydrogen peroxide 10,000 times more quickly and much closer to the planet's surface, where it can easily reach the soil.

Peter Smith, a scientist at the University of Arizona's Lunar and Planetary Laboratory who was not involved in the study, calls the new findings interesting and important.

Until now, he said, scientists have been unable to come up with a mechanism that would put enough oxidants into the soil "to really scour and sterilize" it, as detected by the Viking crafts.

The idea that dust devils might be contributing isn't new, he said, but it had never before gone beyond the realm of brainstorming. Now, he said, "they've actually done the science and have a set of calculations that show it's not just a small effect—it's a very large effect."

Underground Life?

The finding has enormous implications for the search for life on Mars.

"We can't say how life would adapt," Berkeley's Delory said. "The best we can say is that [the Martian surface] is inhospitable to most life as we know it. It's not inconceivable that there are forms of life that thrive under those conditions. We don't know the limits of life."

The University of Michigan's Atreya, however, finds it unlikely that life could exist in the corrosive Martian soils.

"The surface is not where we should be looking," he said.

But he agrees that the search for life should go on.

The peroxide, he says, wouldn't penetrate very deep beneath the surface. And like Earth, Mars gets warmer as you burrow into it: warm enough that there should be liquid water—a necessity for life as we know it—within one to six miles (two to ten kilometers) of the surface.

"If life exists on Mars, it resides below the surface," Atreya said.

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