As Elton John once sang, “Mars is not the place to raise your children; it’s actually pretty damn cold.” But new research suggests that the Martian cold may allow bacteria to survive for up to 280 million years beneath the planet’s surface.
The find raises hopes that traces of ancient life – or even viable organisms in suspended animation – could one day be found on the Red Planet.
In the study, the scientists found that a terrestrial bacterium, Deinococcus radiodurans is so resistant to radiation that it can handle the equivalent of 280 million years of radiation present 33 feet (10 meters) below the Martian surface. The brave little microorganism, which was found to thrive in nuclear reactors on Earth, can even survive for 1.5 million years on the Martian surface, which is constantly bombarded by cosmic and solar radiation.
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The key to this survival is the dry, cold environment of Mars. When it dries and freezes to minus 110.2 degrees Fahrenheit (minus 79 degrees Celsius)—the temperature of dry ice and higher latitude regions of Mars — D. radiodurans “became phenomenally, astronomically resistant to radiation,” said the study’s lead author Michael Dalygeneticist and radiation biology expert at the Maryland Uniformed Services University.
D. radiodurans it has long been known to be a champion of radiation resistance. It is found in the human intestine and in many other places on Earth, and there are even survives for years in the vacuum of space. However, the new research is the first attempt to test the upper limit of radiation resistance of the bacterium when it is in a dried state. Scientists had previously found that the bacterium could withstand 25,000 grams of radiation when in liquid culture, Daly told Live Science. For comparison, a dose of 5 grams would kill a person.
Daly and his colleagues dried and froze D. radiodurans and then bombards the bacteria with gamma radiation and proton radiation, mimicking cosmic radiation from deep space and solar radiation from the sun. They found that dried and frozen D. radiodurans can survive a mind-boggling 140,000 grams of radiation. This is equivalent to the dose of 1.5 million years on the surface of Mars and 280 million years 33 feet below the surface, where the only radiation is from radioactive decay in rocks and minerals.
Organisms survive radiation in two ways, study co-author Brian Hoffman, a chemist at Northwestern University, told Live Science. First, they have multiple copies of their genomes, providing a backup for any bits damaged by radiation. Second, they accumulate large amounts of manganese antioxidants, which trap damaging molecules created by radiation. The capture of these molecules prevents damage to the proteins that perform DNA repair for the body.
“DNA is designed to be repaired, and these manganese antioxidants protect the proteins that do the repair,” Hoffman said.
Life on Mars
D. radiodurans evolved on Earth, where the atmosphere protects the planet and its organisms from the worst radiation. (The bacterium probably evolved to withstand damage during dry spells, and radiation resistance is just a side effect of that evolution, Daly said.) Any Martian bacterium would have to thrive in an environment without this protection, and would probably have to to develop similar resistance to radiation, Hoffman said.
Mars did not have widespread liquid water 2 billion years, so even if ancient life evolved there, 280 million years is still too short to suggest that the planet is host to a host of bacteria just waiting to spring back to life. But because Mars has a very thin atmosphere, meteorites rain down regularly on the planet’s surface, Daly said. The heat and liquid water released by these impacts could potentially awaken dormant bacteria in the subsurface and allow life to temporarily flourish.
Even if this temporary oasis theory isn’t true, the long-lasting potential of bacteria on Mars means that pieces of ancient life could still be present as traces in the rocks, Hoffman said. DNA and other hallmarks of life could exist as fragments even if the organisms were long dead.
The findings also have implications for preventing contamination of Mars with Earth bacteria, according to the study’s authors. Any kind D. radiodurans who rode a rover would likely survive the trip from Earth to the Red Planet. (Other microorganisms, such as E. coli and several Bacillus species, could also survive for thousands of years on the surface of Mars if it dried out and dried out, the researchers found.)
As more missions aim to return samples from Mars to Earth, it will be important to ensure that terrestrial microorganisms are not accidentally downloaded to Mars and then mistaken for aliens, he said John Rummel, senior scientist at the SETI Institute and former NASA Planetary Defense Officer. Rummel was not involved in the new study, but led its editing in the journal Astrobiology.
“The round-trip tourism is a problem here,” Rummel said. “And we have to be careful how we deal with it.”