No, seriously. Scientists have proposed that astrobiologists should luck for Laughing Gas -- Nitrous oxide -- present in a planet's atmosphere as a potential biosignature that could point toward life.
Searching for life elsewhere in the universe is a key for astrobiologists. Thanks to the many technological advancements of the twenty-first century, we are now better equipped than ever to try and answer whether life as we know it may have come into existence on distant alien worlds. This life does not have to be super-evolved- and can just be ordinary, yet-to-evolve lifeforms. But finding evidence of that life can and is very challenging.
We look for a usual set of chemicals that could be a telltale sign that there could be life on a certain world. But what if we were to look for the not-so-ordinary chemicals, and could these help us find out whether there is life on a distant planet or moon? This is a question raised by UC Riverside scientists in their latest paper.
In the new study, scientists at UC Riverside suggest astrobiologists should look for life on other planets around other stars using laughing gas rather than the usual roster of chemicals. Life-indicating chemicals in the atmosphere of a planet, called biosignatures, are typically found in abundance in the atmosphere of Earth today. Biosignatures such as oxygen and methane have received a lot of attention.
Nitrous oxide has received little attention from researchers, but we think that’s a mistake, said Eddie Schwieterman, an astrobiologist at UCR. In an article published in the Astrophysical Journal, this conclusion and the modeling work that led to it are explained in detail. As part of the study, Schwieterman and his colleagues investigated how much nitrous oxide life could possibly produce on a planet like Earth. Using these models, they determined the amount of N2O that could be detected by a telescope such as the James Webb Space Telescope by simulating the planet around different kinds of stars.
According to Schwieterman, nitrous oxide could potentially be detected at levels equivalent to methane or CO2 in star systems like TRAPPIST-1, which provides the best opportunity to study rocky planet atmospheres. Nitrous oxide, or N2O, can be created in several ways by living things. A metabolic process that produces useful cellular energy occurs continuously in microorganisms when they transform other nitrogen compounds into N2O. There are a number of microorganisms that convert nitrogen waste products into nitrates. The nitrates in a fish tank build-up, so it’s necessary to change the water regularly,” Schwieterman explained.
Nevertheless, certain bacteria in the ocean can convert these nitrates into N2O under the right conditions. “Thereafter, the gas leaks into the atmosphere.” It is possible to detect N2O in an atmosphere and still not detect life under certain circumstances. In their modeling, Schwieterman’s team took this into account. Lightning, for instance, produces nitrous oxide in small amounts. However, lightning also produces nitrogen dioxide, which would indicate that the gas was formed by weather or geological processes rather than living organisms.
Others have considered N2O as a biosignature gas but have concluded that it wouldn’t be detectable so far away. Schwieterman explained that the conclusion was reached as a result of the current levels of N2O in the Earth’s atmosphere. Others believe that it would be difficult to detect anywhere else because it isn’t abundant on this planet, which is packed with life. “This conclusion doesn’t account for periods in Earth’s history where ocean conditions would have allowed for the much greater biological release of N2O. Conditions in those periods might mirror where an exoplanet is today,” Schwieterman said.
A common star like the K or M dwarf produces a light spectrum that breaks up the N2O molecule less effectively than our sun. An inhabited world could have a great deal more of this biosignature gas as a result of these two effects combined. In the TRAPPIST-1 system, rocky, Earth-like planets are likely to have atmospheres that are similar to those on Earth, so astrobiologists now need to consider alternative biosignature gases, such as N2O. This idea was put forward to illustrate that we might find a biosignature gas if we look for it,” Schwieterman said.
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