You might never have heard of Methanothermobacter wolfeii= or Methanobacterium formicicum. But they are two common Earth dwellers that emerging research suggests could also thrive on Mars.
Rebecca Mickol is a postdoctoral candidate at the University of Arkansas who is fascinated by the potential for methanogens to survive in Martian conditions. Methanogens are among the planet's oldest life forms, raising the tantalizing prospect that they could have arrived from afar, perhaps aboard an Earth-bound asteroid.
Mickol is interested to know whether methanogens could survive in Mars' brutal conditions, where soils are acidic, temperature swings are extreme, UV radiation is unfiltered by any ozone layer, and water may be inaccessible. The results of experiments that she has conducted so far, including studies of extreme temperature tolerance presented Monday during the 2014 General Meeting of the American Society for Microbiology in Boston, suggest that they could.
"Earth organisms are very robust, and we find them in all sorts of conditions. They could potentially survive on Mars, because there could be small environments somewhere on the planet where these organisms could thrive and grow and begin to populate."
Methanogens are prokaryotes—meaning they are single-celled organisms that lack the tiny organelles and cellular nuclei found in more advanced forms of life. They resemble bacteria and fall into an ancient kingdom of life dubbed Archaea, which are all around us. Even inside us. They can survive in conditions that would be too hostile for their more contemporary evolutionary counterparts, including extremely hot, subterranean, and oxygen-free environments. They don't need sunlight or nutrients. All of this helps them revel in marshes, cattle, and human guts, where they produce methane—a gas that's also found on Mars.
"Earth organisms are very robust, and we find them in all sorts of conditions," Mickol says. "They could potentially survive on Mars, because there could be small environments somewhere on the planet where these organisms could thrive and grow and begin to populate. That’s why the Planetary Protection Program exists at NASA, so that we make sure we're not contaminating Mars. If we ever bring back a sample, we don’t want to contaminate Earth, either."
Mickol selected the two species of methanogens because they are already well understood by science and because one prefers middling temperatures, ideally 37 degrees Celsius, while the other likes it hot—55 C. She placed the organisms in test tubes, then repeatedly ratcheted the temperatures up and down over as many as 245 days. Temperatures were lowered to as little as -80 C and back up as high as the species' ideal growing temperatures. She discovered that they just wouldn't die. Some of the strains didn't just survive—they actively grew even as temperatures fell to nearly freezing.
"The survival of these two methanogen species exposed to long-term freeze/thaw cycles suggests methanogens could potentially inhabit the subsurface of Mars," Mickol writes in an abstract describing her results, which have not yet been peer-reviewed.
Mickol previously conducted experiments that showed some methanogens could survive in low pressures similar to those found on Mars.
"Approaching Martian pressure, they can survive," Mickol says. "The next step is to combine the low temperature and low pressure to better mimic Martian conditions."