Bacteria that have been dried and frozen, as they would most likely be just beneath the surface of Mars, can survive the intense radiation that bombards the Red Planet for hundreds of millions of years.
|This extremophile bacteria can withstand extreme radiation MICHAEL J DALY/SCIENCE PHOTO LIBRARY|
Microorganisms may be able to survive just beneath the surface of Mars for much longer than scientists previously thought. Researchers discovered that dried-up bacteria could survive in Mars-like conditions for up to 280 million years, increasing our chances of finding evidence for them if Mars ever hosted life.
Most previous experiments to see if microorganisms could survive the intense radiation on Mars used hydrated bacteria at room temperature, with the longest-lived strains thought to be able to survive for up to a million years. Brian Hoffman of Northwestern University in Illinois and his colleagues took a different approach, desiccating and freezing a variety of bacteria and yeast before subjecting them to radiation similar to that experienced by a buried life form on Mars and measuring the damage.
"When you get rid of the water and cool everything down, there's this phenomenal multiplication of resistance," Hoffman says. It is similar to freeze-drying food to extend its shelf life. Mars is dry and cold, so any bacteria found there are likely to be as well. The radiation caused so little damage to the researchers' samples that they estimated the bacteria could live for up to 280 million years.
More information: If Mars contains life, its total mass is 10,000 times that of Earth.
If the freeze-dried bacteria were warmed and exposed to water during that time, they would come to life. "It opens up the possibility that if a meteor with some water comes down and splashes on the surface, it could regenerate," Hoffman says. "The probability that it's still alive now has risen from zero to the tiniest thing you can imagine - it's non-zero, but it ain't big." Mars is thought to have dried up around 3 billion years ago, so even the hardiest bacteria are most likely extinct by now.
This longevity may make it easier to find preserved evidence of any bacteria that once lived on Mars, but it also means that any contamination with Earthly organisms will be nearly permanent.
"How do we know whether what we find was there before we got there or whether it was something we deposited if we contaminate the area that we land in?" Hoffman asks. "If we can't tell what's ours and what's theirs, it's impossible to tell if there was life there."