Methane—a key ingredient in delightful things like swamp gas, flatulence, and fossil-fuel emissions—could also prove to be a key biosignature, i.e., evidence of extraterrestrial life. Thus, the gas is top-of-mind for scientists preparing to receive an influx of data from the James Webb Space Telescope. According to NASA, one of Webb's main functions is to probe for biosignatures in the atmospheres of distant exoplanets, and its infrared detectors should be good at measuring the presence of methane (the same isn't true for oxygen). That alone is not big news, but a related study from astronomers at UC Santa Cruz could smooth the path to one of humankind's biggest discoveries.
There are plenty of nonbiological reasons why methane can accumulate on rocky planets, including volcanic activity. As such, "we wanted to provide a framework for interpreting observations, so if we see a rocky planet with methane, we know what other observations are needed for it to be a persuasive biosignature," says lead author Maggie Thompson, per a press release. As Reuters reports, atmospheric methane is unstable and wouldn't last long at a consistent level unless it was constantly being replenished. If that replenishment comes from a nonbiological source—like a volcano—there would be chemical evidence of that, Thompson explains.
For example, volcanoes release both methane and carbon monoxide, but "biological activity tends to devour carbon monoxide and reduce its atmospheric concentrations," per the press release. Thompson and her colleagues conclude that the presence of atmospheric methane would signal "a strong indication of life if the atmosphere also has carbon dioxide, methane is more abundant than carbon monoxide, and extremely water-rich planetary compositions can be ruled out." (Read more James Webb Space Telescope stories.)