Methane in Context as a Powerful Biosignature on Exoplanets Now Accessible through JWST

Credit: NASA.

The Copernican principle, inspired by the mid-16th-century idea of Nicolaus Copernicus that Earth is not the center of the universe, states that we may not be alone in the universe and that, in fact, there is nothing special about our species. The James Webb Space Telescope (JWST) is the most powerful infrared telescope to date with a spectral range of 0.6-28 micrometers versus 0.8-2.5 micrometers for the Hubble Space Telescope, and JWST has a field of view approximately 15 times larger than that of Hubble. With its recent launch, exoplaneteers are eager to study even more exoplanets in greater detail than ever before, allowing compelling new biosignatures to be observed for the first time.

A new study by Joshua Krissansen-Totton, Maggie Thompson, Max Galloway, and Jonathan Fortney from University of California, Santa Cruz, describes methane (CH4) in the context of other biosignature gases as a potential biosignature now accessible through the recently launched JWST. In the Archean era, when life began on Earth, abundant atmospheric methane coexisted with CO2, with the ratio CO:CH4 << 1. Without the presence of life to replenish it, methane would ordinarily react to form ammonium and bicarbonate in the presence of CO2, N2, and liquid water. Other abiotic sources of methane, including a reduced mantle, impacts, extensive hydrothermal systems, and a warm Titan analog, would have different coexisting gases that are also detectable using JWST and ground-based Extremely Large Telescopes in the 2020s.

However, given the possibility of false positives, multiple independent lines of evidence will be required for robust life detection, such as temporal variations indicative of seasonal metabolic activity. Detection of life is likely to be an emergent process through decades of debate and future missions. Nevertheless, JWST should be able to make the first tentative detections of biosignature gases such as CH4 to test how common biosignatures are and, in combination with other gases like O2 and CO2, to test how common abiotic sources are. READ MORE