US researchers have concluded that nitrogen oxide (I), or laughing gas, in the atmospheres of exoplanets could act as a marker for the presence of life. This data will be taken into account when the James Webb Space Telescope receives information on the atmospheres of rocky exoplanets that resemble Earth.
Scientists at the University of California, Riverside, USA, have suggested that the typical list of chemicals used by astrobiologists to search for life on other planets is missing nitric oxide (I), or laughing gas (N2O). The results of the study that led them to this conclusion are published in The Astrophysical Journal.
The list of chemical compounds in the planet's atmosphere that could indicate the presence of life usually includes gases that are abundant in Earth's atmosphere today. However, the cheerful gas has always received very little attention.
Now researchers have estimated how much nitrous oxide could be produced by living things on an Earth-type planet. They then created computer models of such a planet orbiting different types of stars and determined the amount of N2O that could be detected by an observatory like the James Webb Space Telescope.
To give an example, the authors looked at the stellar system TRAPPIST-1, located in the constellation Aquarius and well suited to the study of rocky planets in the star's habitable zone. Scientists have concluded that in TRAPPIST-1, nitrous oxide is potentially detectable at levels comparable to carbon dioxide or methane.
In the Earth's atmosphere, N2O comes from various bacteria, but this is not the only way. The authors factored this into their modelling. Small amounts of nitrous oxide are created by lightning, for example. However, together with N2O, lightning also produces nitrogen dioxide, which can help astrobiologists distinguish between weather conditions and the biological processes that create this gas.
In addition, it was thought that N2O would be difficult to detect at long distances. But this conclusion is based on today's concentrations of N2O in the Earth's atmosphere: it does not take into account periods in our planet's history when conditions contributed to a much larger biological release of N2O.
The authors also reported that the radiation of stars of spectral classes K and M (the latter includes the star TRAPPIST-1) destroy N2O molecules much less effectively than the Sun. The combination of these two effects may significantly increase the N2O concentration in the atmospheres of potentially habitable planets.
