The James Webb Space Telescope may be able to identify nitrous oxide in the atmospheres of exoplanets as a biosignature.
Finding extraterrestrial life is a serious endeavour. Before now.
In order to find biosignatures in the atmospheres of exoplanets, astronomers should use the James Webb Space Telescope (JWST) to hunt for nitrous oxide (N2O), also known as laughing gas.
Oxygen and methane have received a lot of consideration as biosignatures, according to main scientist Eddie Schwieterman of the University of California, Riverside (opens in new tab). Nitrous oxide hasn’t received much attention from researchers, but we believe that may be a mistake.
Nitrous oxide is a natural waste product of life on Earth. Nitrogen molecules are taken up by microorganisms and converted into nitrates, which releases metabolic energy. Every fish owner is aware of this, which is why it’s important to routinely clean fish tanks in order to get rid of extra nitrates that accumulate over time.
However, in other situations, some bacteria prefer nitrates and further break them down metabolically to form nitrous oxide. Since nitrous oxide creates absorption lines at near- and mid-infrared wavelengths that may be seen by JWST, its abundance in a planet’s atmosphere would be a powerful biosignature.
The amount of nitrous oxide that would need to be present in the atmosphere of one of the planets in the TRAPPIST-1 system, located 39 light-years away, for JWST to detect it, was calculated by Schwieterman and his team. They discovered that nitrous oxide would be observable in quantities comparable to those of carbon dioxide and methane in the atmosphere of Earth.
However, it would appear that there is an issue at first glance. Despite all of the life on Earth, nitrous oxide production is less than that of carbon dioxide and methane. What gives, then?
This, according to Schwieterman, “doesn’t account for times in Earth’s history where ocean conditions would have permitted for far more biological emission of N2O.” He is talking to times that occurred between 2.5 billion and 540 million years ago, during the Proterozoic Eon. The Proterozoic Eon spans from the beginning of complex life until the oxydation of the Earth’s atmosphere. “Conditions at past times might have mirrored the current location of an exoplanet,” Schwieterman continued.
Furthermore, planetary systems around cool, dim M-dwarf stars, like TRAPPIST-1, have an advantage since they don’t emit the Sun’s abundant radiation, which can degrade nitrous oxide molecules.
Nitrous oxide can also be created physically, for example, when lightning causes chemical interactions with airborne molecules. However, as lightning also produces nitrogen dioxide, the existence of both gases in an exoplanet’s atmosphere in comparable abundances would be a clear indication that the planet is stormy rather than habitable.