Nitrous oxide, telltale sign of life on other worlds?

Chemical compounds in a planet’s atmosphere that could indicate life, called biosignatures, often include gases that are abundant in Earth’s atmosphere today and can be produced by biological processes.

The two gases that have received the most attention as biosignatures are oxygen and methane. Very few researchers have seriously considered nitrous oxide, and this may be a mistake.

Eddie Schwieterman’s team, from the University of California at Riverside, United States, has carried out a study on nitrous oxide as a biosignature and on the ability to detect it on exoplanets (planets outside our solar system).

Schwieterman and his colleagues began by calculating how much nitrous oxide living things could produce on an Earth-like planet. Once the calculation was done, they made digital models that simulated that planet around different types of stars and determined the amounts of nitrous oxide (N2O) that an observatory such as the James Webb Space Telescope could detect.

“In a star system like TRAPPIST-1, the closest and best system for observing the atmospheres of rocky exoplanets, nitrous oxide could potentially be detected at levels comparable to carbon dioxide or methane,” says Schwieterman.

The TRAPPIST-1 system, from which we could soon obtain more information about the atmospheres of some of its planets, of a rocky type like Earth, thanks to the James Webb Space Telescope. There is a possibility that nitrous oxide could be detected in the atmosphere of one of them, which could indicate the presence of life forms. (Illustration: NASA JPL / Caltech)

Living things can create nitrous oxide in multiple ways. Many microorganisms constantly transform other nitrogen compounds into nitrous oxide, a metabolic process that can produce useful cellular energy.

Under certain circumstances, nitrous oxide could be detected in an atmosphere and still not indicate the existence of life. Schwieterman’s team took this into account in their work with digital models. A small amount of nitrous oxide is created by lightning, for example. But in addition to nitrous oxide, lightning also creates nitrogen dioxide, which may offer astrobiologists a clue that meteorological or geological, not biological, processes created the gas.

Other scientists who have considered nitrous oxide as a biosignature often conclude that it would be difficult to detect from so far away. Schwieterman argues that this conclusion is based on the concentrations of nitrous oxide in Earth’s atmosphere today. Since there is not much nitrous oxide on our planet now, which is teeming with life, it is easy to assume that it would be difficult to detect on other worlds as well.

“This conclusion does not take into account the periods of the Earth’s history in which the oceanic conditions should have allowed a much greater biological release of nitrous oxide. The conditions prevailing in those periods could reflect the current situation of an exoplanet”, Schwieterman reasons. .

Schwieterman also argues that stars of spectral type K and red (M-type) dwarfs, very common in the universe and less luminous than the Sun, produce a light spectrum that is less effective at breaking down the nitrous oxide molecule than our own. Sun. This could make the amount of nitrous oxide present on an inhabited world much higher than predicted.

The research team believes that now is the time for astrobiologists to pay attention to alternative biosignaling gases like nitrous oxide, as the James Webb telescope could soon send back highly detailed information about the atmospheres of rocky Earth-like planets in the TRAPPIST-1 system.

The study is titled “Evaluating the Plausible Range of N2O Biosignatures on Exo-Earths: An Integrated Biogeochemical, Photochemical, and Spectral Modeling Approach.” And it has been published in the academic journal The Astrophysical Journal. (Font: NCYT by Amazings)