“We might actually select for these organisms,” said Adam Johnson, a graduate student at Indiana University and lead author of a paper to be published in the journal Icarus. “They would be the most likely thing to be able to survive.”

Johnson and colleagues subjected some of Earth’s toughest life forms from the most extreme environments they could find to 40 days in a mockup Mars environment.

The subjects included bacteria from Siberian permafrost; single-celled microorganisms called haloarchaea from briny saltwater in Mexico; yeastlike organisms from cold saline springs in the Canadian arctic; and tardigrades (also known as water bears), the world’s toughest multicellular animal, which have been known to survive trips into space.

“We threw a lot of organisms at the experiment,” Johnson said. “A lot of studies just focus on one, but we really just threw the kitchen sink at it.”

The researchers cooked up a batch of simulated Martian soil, called regolith, from volcanic basalt rocks taken from two different outcrops in Oregon. They baked the mixture for 12 hours at 750 degrees Fahrenheit to make sure it was free of organic materials.

Then they mixed carefully measured samples of the organisms into the soil, and let the concoction sit in a glass chamber meant to simulate the Martian atmosphere for a week. After that first week, Johnson set the chamber to mimic the daily temperature variations, solar cycle and ultraviolet radiation at the Martian surface for 40 days.

Earlier studies had found that the single biggest threat to Earthly microbes was ultraviolet radiation, but being buried in just a millimeter of soil could protect organisms enough to keep them alive.

Johnson and colleagues expected organisms that like extreme cold, called psychrophiles, to fare best in the negative-40-degree Martian nights.

Surprisingly, cold-loving critters dropped off quickly in their first week in the chamber, when temperatures were held at a balmy 50 degrees Fahrenheit.

“Really temperature and atmosphere doesn’t matter,” Johnson said. “It seemed to be the actual conditions of the regolith and [the organisms] themselves that determined the chance of survival.”

Most of the creatures died from drying out, or from the harsh chemical conditions in the fake Martian soil.

“They become almost mummified,” Johnson said. “It looks like organisms go almost into a freeze-dried type state.”

The only organisms that made it were the salt-loving haloarchaea from Mexico, and the hardy tardigrades. Tardigrades can slow down their metabolisms by a factor of 10,000 under harsh conditions, allowing them to dry up without dying. Based on their success in the simulated Mars chamber, Johnson thinks they could last more than 300 days on Mars.

“This is the first study where we’ve actually shown that an organism could potentially last for several hundred days on the surface of Mars,” he said.

Current techniques for sterilizing spacecraft use dry-heat treatments and chemicals similar to those that could be produced in the Martian soil. Whatever organisms survive those treatments are also the most likely things to survive and thrive once they reach Mars, Johnson said.

“Everybody knows that this is not the greatest way to go about it, but that’s the way they do it,” said astrobiologist Rocco Mancinelli of the SETI Institute, a coauthor of the paper. “I personally think it has to be revamped.”

“This paper points out the need for ongoing re-examination and updating of sterilization and detection methods used for planetary protection purposes during cleaning and preparation of spacecraft,” said Margaret Race of the SETI Institute, who studies how best to avoid contaminating Mars with earthly life, and vice versa, but was not involved in the new study. “We are continuing to find microorganisms that surprise us in their hardiness.”

Image: Brett’s Blog

See Also:

• Invertebrate Astronauts Make Space History
• Hot Spot for Life Found on Ancient Mars Volcano
• 1976 Look at Mars Soil May Have Missed Life’s Building Blocks
• NASA: Mars Soil Could Support Extreme Life Forms, Maybe
• Life Hunters Target Methane Plumes on Mars
• Life Thrives in Earth’s Most Mars-Like Environment

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Authors: Lisa Grossman

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