Biosignatures & Paleobiology

Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres?

By Keith Cowing
Status Report
December 28, 2023
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Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres?
Intensity of key gas isotopologues, which could potentially be metabolically fractionated. The wavelength range shown on the x-axis includes the strongest features of each isotopologue relevant to JWST. The 13 CO2 and 12 CO2 isotopologues (in green) are both the strongest absorbers and the most well spectrally separated, making them the best isotopologue pair for spectroscopic detection with JWST. — Life

Isotopologue ratios are anticipated to be one of the most promising signs of life that can be observed remotely. On Earth, carbon isotopes have been used for decades as evidence of modern and early metabolic processes.

In fact, carbon isotopes may be the oldest evidence for life on Earth, though there are alternative geological processes that can lead to the same magnitude of fractionation. However, using isotopologues as biosignature gases in exoplanet atmospheres presents several challenges. Most significantly, we will only have limited knowledge of the underlying abiotic carbon reservoir of an exoplanet.

Atmospheric carbon isotope ratios will thus have to be compared against the local interstellar medium or, better yet, their host star. A further substantial complication is the limited precision of remote atmospheric measurements using spectroscopy.

The various metabolic processes that cause isotope fractionation cause less fractionation than anticipated measurement precision (biological fractionation is typically 2 to 7%). While this level of precision is easily reachable in the laboratory or with special in situ instruments, it is out of reach of current telescope technology to measure isotope ratios for terrestrial exoplanet atmospheres.

Thus, gas isotopologues are poor biosignatures for exoplanets given our current and foreseeable technological limitations.

Ana Glidden, Sara Seager, Janusz J. Petkowski and Shuhei Ono
Life 2023, 13(12), 2325; DOI: 10.3390/life13122325

Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres?, Life (open access)


Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻