The Mars Odyssey spacecraft has discovered a curious sight on the red planet’s northern planes: mud volcanoes spurting methane gas and sediment up to the icy surface. Think about that for a second. What do you need to have mud? And what produces methane gas? That’s right, water and animals.

This is not to say the Martian underworld is overrun with jersey cows or giant sand worms. Animals aren’t the only source of methane, but scientists theorize that the gas could indeed be due to thriving microbes several miles beneath the Martian surface. Down there, warmer temperatures could theoretically permit things like mud and life to exist.

This news, reported in a New Scientist article, comes on the heels of a recent geological study on Earth supporting the notion that ancient, subterranean extremophiles might have survived the catastrophic celestial bombardment of the Earths’ crust 3.9 billion years ago.