Currently, the best way to search for alien life in other star systems is by looking for biosignatures: the presence of specific molecules in the atmospheres of distant worlds. Many substances are being considered for such a role – oxygen is the main candidate, and methane as well. The work on phosphine as a potential biosignature led to a whole debacle about Venus and life in its clouds.
Now, researchers from the University of California, Riverside have made the case for another type of gas: nitrous oxide (N2O), commonly known as laughing gas. There are many biological processes that produce this substance, and the models produced by the team suggest that it may be possible to detect it in the atmospheres of nearby exoplanets using JWST.
Fewer researchers have looked seriously at nitrous oxide, but we think this may be wrong.
“In a star system like TRAPPIST-1, the closest and best system for observing the atmospheres of rocky planets, you could potentially detect nitrous oxide at levels comparable to CO2 or methane,” lead author Eddie Schwieterman, an astrobiologist in UCR’s Department of Earth and Planetary Sciences, said in a statement.
Nitrous oxide production is mainly due to microorganisms – some small creatures can use nitrates to fuel their cellular metabolism, releasing laughing gas in the process.
“Life produces nitrogenous waste that is converted by certain microorganisms into nitrates. In a fish tank, these nitrates build up, so you have to change the water,” Schwieterman added. “However, under the right conditions in the ocean, certain bacteria can convert these nitrates into N2O. The gas then leaks into the atmosphere.’
This is where telescopes might spot it. Previous studies have dismissed the possibility of seeing nitrous oxide because, on modern Earth, it is not very abundant. However, the team says this conclusion does not take into account how exoplanets may have conditions more suitable for creating this gas. Also, stars fainter than the Sun are less likely to break up this gas.
“This conclusion does not take into account periods in Earth’s history when ocean conditions would have allowed much greater biological release of N.2O. Conditions in those periods may reflect where an exoplanet is today,” Schwieterman said.
The team is convinced that nitrous oxide is a serious biosignature candidate to be explored elsewhere in the galaxy.
“There has been a lot of thinking about oxygen and methane as biosignatures. Fewer researchers have looked seriously at nitrous oxide, but we think that might be wrong,” Schwieterman concluded.
The work was published today in The Astrophysical Journal.