How a Simple Gas Could Help Us Find Alien Life

Scientists say they may be able to spot life on other planets by looking for signs of methane—the notorious greenhouse gas that's burped out by cows.

When it comes to finding habitable planets, it's tempting to think that oxygen would be the key environmental signature that scientists would look for. It's necessary for most life on Earth.

The problem is that oxygen would be hard to detect on other planets using the James Webb Space Telescope, the recently launched telescope that's expected to aid scientists in their search for extra-terrestrial life.

Webb wasn't originally designed to scan distant planets for oxygen, and its instruments are therefore not set up in a way that will readily detect it. Webb's instruments can, however, spot methane.

Methane is an abundant gas on Earth and is also a greenhouse gas. It's produced in huge quantities by human activity, including landfills, oil and natural gas systems, agriculture and mining. It accounts for 20 percent of global greenhouse gas emissions, according to the U.S. Environmental Protection Agency (EPA).

Animal Flatulence

The gas is also a component in animal burping and flatulence. In Australia, for instance, livestock alone accounts for 56 percent of all of the country's methane emissions.

Methane might be a problem on Earth, but it's useful for scientists looking for signs of life elsewhere.

"If you detect a lot of methane on a rocky planet, you typically need a massive source to explain that," Joshua Krissansen-Totton, a researcher in the Department of Astronomy and Astrophysics at the University of California, Santa Cruz, said in a press release.

"We know biological activity creates large amounts of methane on Earth, and probably did on the early Earth as well because making methane is a fairly easy thing to do metabolically."

While methane could be useful in the search for life, it's only part of the puzzle. It can also be produced by natural, non-biological processes such as through volcanic activity.

Scientists might therefore look for a planet with an atmosphere rich in both methane and carbon dioxide and with little to no carbon monoxide—a gas that tends to be consumed by biological activity, according to the UCSC statement.

Scientists have been looking at ways to assess true methane-related signs of life and rule out what might be a false positive.

"Methane is one piece of the puzzle, but to determine if there is life on a planet you have to consider its geochemistry, how it's interacting with its star, and the many processes that can affect a planet's atmosphere on geologic timescales," said Maggie Thompson, an astronomy and astrophysics researcher at UCSC who led a new study into the matter.

A file image of an exoplanet—a planet outside of the solar system—in space. Scientists may look for methane as a sign of life on other worlds. dima_zel/Getty