Keep Mars Clean!

Now that NASA has established the presence of liquid water on Mars—an announcement that brings with it the tantalizing possibility of life on the Red Planet—it’s even more important that we not contaminate the place with microbes hitchhiking in on landers. Not only would that confuse the search for life, it might also allow Earth microbes to colonize Mars, kind of like Mars Attacks!, only in reverse and without laser guns.

Of all the spacecraft that have landed on Mars, only the two Viking landers in 1976 were thoroughly sterilized. That process involves baking at high temperatures, meaning everything on board has to be able to withstand the heat, adding expense and complexity.

Vincent Chevrier, an assistant research professor in U of A’s Arkansas Center for Space and Planetary Sciences, is studying

Mars landers usually aren't sterilized to prevent microbial hitchhikers from Earth

Mars landers usually aren’t sterilized to prevent microbial hitchhikers from Earth. Photos courtesy of NASA.

the problem of keeping Mars tidy. Last week, Chevrier received a $465,000 NASA grant for a four-year project to study whether microbes from Earth can survive in Martian conditions. If it turns out the microbes like it on Mars, future landers may have to be sterilized before they can approach potentially habitable areas. Microbes from Earth that can survive on Mars might also tell us how to look for life native to the planet.

This is the fourth NASA grant Chevrier has received in the last month to study planetary environments. In all, the grants provide more than $1.6 million for research on the environments of Mars, Venus and Saturn’s largest moon, Titan. Details of the other grants can be found here. He has long studied Mars with NASA support and in May published his findings of briny water on Mars in Nature Geoscience.

Liquid water on Mars is found in dark streaks a few yards wide running down the sides of craters, mountains and canyons. Scientists call them recurring slope linae, or RSLs, and there are thousands of them. They grow in the Martian summer and shrink in the Martian winter.

However, Mars is cold all the time; the average temperature is about 70 degrees below zero Fahrenheit. The RSLs flow because they are made up of sulfate-rich brines with a freezing point much lower than pure water. Given the abundance of sulfates on Mars, Chevrier chose to study Earth-grown, sulfate-reducing bacteria as a possible contaminant.

“Will it adapt,” he asks, “or just die?”

To find out, he’ll try to grow bacteria in pressure vessel that simulates conditions on the surface of Mars: high concentrations of sulfates, low atmospheric pressure and very cold temperatures. There’s some evidence that life can exist in such extreme environments. Previous studies have shown that common bacteria could survive in the shallow subsurface of Mars, and lichen from Antarctica could live in temperatures as low as -40 degrees Fahrenheit.

But no one has studied whether sulfate-reducing bacteria can thrive in conditions found on Mars. No matter the results, it’s a question worth asking. “Survival is a very interesting possibility, and we would be delighted to observe it,” he says.


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