A group of microorganisms called methanogens found in marshes and in the guts of cattle produce the natural gas on our planet. Methanogens don't need oxygen or photosynthesis to live, so the most likely way for them to survive on Mars is if they're found underneath the surface, protected from the red planet's high levels of ultraviolet radiation.

Since we can't exactly fly cows to Mars for an experiment, the scientists grew microbes in test tubes with liquids representing fluids that could have flowed underneath the Martian surface long ago. They also replicated the extremely low atmospheric pressures of the area underneath the Martian surface within each test tube. Plus, they subjected the organisms to freezing temperatures to emulate the planet's.

[Image credit: Rebecca Mickol]

After almost a year of experiments on four different species, the scientists found that all of them managed to survive under those harsh conditions for three to 21 days. Mickol warned, however, that the methane on Mars could have been a product of volcanism and other factors. Their study merely explores the possibility of "life -- bacteria or tiny microorganisms -- somewhere else in the Universe." After all, there's an abundance of life even in extremely unfriendly environments here on Earth.