Methane could be the first detectable indication of life beyond Earth

If life is abundant in the universe, atmospheric methane may be the first sign. Although nonbiological processes can generate methane, a new study by scientists at UC Santa Cruz establishes a set of circumstances in which a persuasive case could be made for biological activity as the source of methane in a rocky planet's atmosphere.

This is noteworthy because methane is one of the few signs of life that could be easily detected with the James Webb Space Telescope, which will begin observations later this year.

Oxygen is often talked about as one of the best biosignatures, but it is likely to be hard to detect with the JWST.

There was not an up-to-date assessment of the planetary conditions needed for methane to be a good biosignature.

The study looked at a variety of non-biological sources of methane and assessed their potential to maintain a methane-rich atmosphere. These include volcanic eruptions, reactions in settings such as mid- ocean ridges, and comet or asteroid impacts.

Methane is a biosignature because of its instability in the atmosphere. High levels of atmospheric methane are maintained because photochemical reactions destroy it.

If you detect a lot of methane on a rocky planet, you need a massive source to explain it.

Nonbiological sources wouldn't be able to produce that much methane without also generating clues to its origins. Carbon monoxide and methane would be added to the atmosphere by outgassing from volcanoes. The researchers found that nonbiological processes can't produce atmospheres rich in methane and carbon dioxide.

The study emphasizes the need to consider the full planetary context in evaluating potential biosignatures. If the atmosphere has carbon dioxide, methane, and/or water, atmospheric methane is more likely to be a strong indication of life than carbon dioxide, methane, and/or water.

One molecule is not going to give you the answer, you have to take into account the planet's full context.

The study provides guidelines for assessing methane biosignatures and considers a variety of possibilities for false positives.

Krissansen-Totton said there are two things that could go wrong, one is misinterpreting something as a biosignature and the other is overlooking something that is a real biosignature.

There is still a lot of work to be done to fully understand any future methane detections. Future work should try to anticipate and quantify more unusual mechanisms for nonbiological methane production.

The authors of the paper include Thompson and Krissansen-Totton, as well as Jonathan Fortney, Myriam Telus, and Nicholas Wogan.

More information: The case and context for atmospheric methane as an exoplanet biosignature, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2117933119 Journal information: Proceedings of the National Academy of Sciences Citation: Methane could be the first detectable indication of life beyond Earth (2022, March 28) retrieved 28 March 2022 from https://phys.org/news/2022-03-methane-indication-life-earth.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.