We Could Track Alien Life With This List of Cosmic Farts

Every living thing, from the grass to your roommate, releases gas into the atmosphere. When it's a human releasing gas in an unventilated car, it's disgusting. But in the deepest depths of the galaxy, it could be how we discover extraterrestrial life — and a team at the Massachusetts Institute of Technology just gave humanity a cheat sheet.

Sara Seager, professor of planetary science and physics at MIT and lead on a corresponding paper in the journal Astrobiology, spent three years building a list of pretty much any known molecule that could be a gas.

Using a light-measurement technique called spectroscopy, astronomers can see the atmospheric gases of planets light-years away. Some of those gases indicate signs of current or past life on a planet; they're called biosignatures.

If aliens looked at our planet from light-years away, they could analyze the light passing through our atmosphere, tell that it contains oxygen and infer there's a biosphere — a place occupied by living organisms.

Source: Giphy

But there is an incredible number of gas molecules that could indicate signs of life. That's where the cheat sheet comes in.

"What we've done is [create] a list to work through all the scenarios," Seager said in a phone call on Monday.

Basically, a planetary scientist could offer a scenario that creates gases, like a volcano. Astronomers would check the byproducts of a volcano against what they see on an alien surface. If the byproducts line up with a volcano, it's just geochemistry at work.

If they don't, it might be something else.

Think of our own planet: Methane is released from vents in the ocean floor, and the gas winds up in the atmosphere. To anyone off-planet looking at Earth, that could be mistaken for life, since methane in the atmosphere could also come from cows or burps. And that's where a giant gray area exists.

Source: Giphy

"It's like forensic analysis," Seager said. "We won't be 100% sure. The unknown is if the gas is indeed produced by life."

The list includes 14,000 molecules, and about a quarter of them are known to be produced on Earth. A couple thousand of them are biogenic, or created by life on Earth. But this all assumes life on other planets is carbon-based, like our own. That's another unknown.

"Still, you can hedge your bets about what elements you start working on," Seager said. 

According to Seager, this is still another 10-odd years of work, identifying molecules that might be false positives. Even then the research probably won't lead to a Close Encounters of the Third Kind scenario. But it would push humanity light-years toward understanding the biology that makes living things possible.

"Finding evidence of an exo-biosphere is so important — that's alien grass and plants," Adam Frank, a professor of physics and astronomy at the University of Rochester who wasn't involved in the paper, said in a phone interview. "To find a planet with a biosphere would be one of the greatest scientific finds in the history of human beings."