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Laughing Gas Could Be a Sign of Life on Distant Planets

No joke. The search for extraterrestrial life could take a funny turn.

This artist's concept illustration shows Trappist-1, a intriguing star system with Earth-size planets.
NASA/JPL-Caltech/R. Hurt (IPAC)

Humanity's quest for life beyond Earth involves investigating planets in our own solar system (hello, Mars) and exoplanets outside of it. A team of astrobiologists has proposed looking for nitrous oxide, known as laughing gas, as a possible indication of life on distant worlds.

Nitrous oxide may have a reputation as a giggle-inducing gas for humans, but this proposal is no laughing matter. It's about expanding what we look for when we're searching for biosignatures -- chemical compounds that could indicate the existence of life -- in the atmospheres of exoplanets.

"There's been a lot of thought put into oxygen and methane as biosignatures. Fewer researchers have seriously considered nitrous oxide, but we think that may be a mistake," said astrobiologist Eddie Schwieterman in a University of California, Riverside statement on Tuesday. Schwieterman is lead author of a paper on the topic published in The Astrophysical Journal this week.

Nitrous oxide can be generated by microorganisms on Earth, but it's not currently very concentrated in our own atmosphere. That suggests it might not be worth looking for on exoplanets. "This conclusion doesn't account for periods in Earth's history where ocean conditions would have allowed for much greater biological release of N2O," Schwieterman said. "Conditions in those periods might mirror where an exoplanet is today." 

Schweitermen's team ran computer models to simulate how living organisms might generate nitrous oxide on other planets and discovered scenarios where the gas could act as a notable biosignature. The trick is we would have to look for it.

The researchers suggest observatories like the James Webb Space Telescope, which is able to study exoplanet atmospheres, could be used to search for nitrous oxide. The nearby star system Trappist-1, home to some intriguing Earth-size planets, would be a good testing ground for the idea.