Challenges in the detection of gases in exoplanet atmospheres
2025/04/30 by Luis Welbanks, Matthew C. Nixon, Welbanks, Luis +30 · 11 voices · 8 citations
Physics and Astronomy · #Stellar, planetary, and galactic studies #Astro and Planetary Science #Astrophysics and Star Formation Studies
paper · pdf · doi:10.1038/s41550-025-02730-4
Abstract
Claims of detections of gases in exoplanet atmospheres often rely on comparisons between models including and excluding specific chemical species. However, the space of molecular combinations available for model construction is vast and highly degenerate. Only a limited subset of these combinations is typically explored for any given detection. As a result, apparent detections of trace gases risk being artifacts of incomplete modeling rather than robust identification of atmospheric constituents, especially in the low signal-to-noise regime. Using the sub-Neptune K2-18 b as a case study, we show that recent biosignature claims vanish when the model space is expanded, with numerous alternatives providing equally good or better fits. We demonstrate that the significance of a claimed detection relies on the choice of models being compared, and that model preference does not in itself imply the presence of a specific gas. We recommend treating model comparisons instead as relative adequacy tests, which should be supported by theoretical predictions and complementary metrics of statistical significance in order to attribute a signal to a particular gas.
Citations
- Insufficient evidence for DMS and DMDS in the atmosphere of K2-18 b
- A Systematic Search for Trace Molecules in the Atmosphere of Exoplanet K2-18 b
- Are there Spectral Features in the MIRI/LRS Transmission Spectrum of K2-18b?
- New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI
- Enabling Robust Exoplanet Atmospheric Retrievals with Gaussian Processes
- A Comprehensive Reanalysis of K2-18 b's JWST NIRISS+NIRSpec Transmission Spectrum
- Carbon-bearing Molecules in a Possible Hycean Atmosphere
- Identification of carbon dioxide in an exoplanet atmosphere
- The Revised TESS Input Catalog and Candidate Target List
- Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects
- HITEMP, the high-temperature molecular spectroscopic database
- The Chemical Composition of the Sun
- The James Webb Space Telescope
- H 2 , He, and CO 2 line-broadening coefficients, pressure shifts and temperature-dependence exponents for the HITRAN database. Part 1: SO 2 , NH 3 , HF, HCl, OCS and C 2 H 2
Cited by
Discussions
- A new, thorough reanalysis of the data that led to claims of biosignatures on K2-18b from @luiswel.bsky.social & friends - a nicely written lesson on why this stuff is hard. They find no significant e [bsky, 121 points, 6 comments]
- The K2-18b saga deepens with a great new paper out today by @luiswel.bsky.social (arxiv.org/abs/2504.21788). Turns out hydrocarbons can explain K2-18b's new JWST MIRI spectrum *without* the need to in [bsky, 97 points, 1 comments]
- #arXiv The Challenges of Detecting Gases in Exoplanet Atmospheres https://arxiv.org/abs/2504.21788 for K2-18b, numerous alternative models without potential biosignature gases provide equivalent or be [bsky, 8 points, 0 comments]
- If you're interested in the gory details of all 90 hydrocarbons we tested, or the subtleties of Bayesian statistics, check out the full paper which we have submitted for peer review: arxiv.org/abs/250 [bsky, 3 points, 0 comments]
- arxiv.org/abs/2504.21788 Oh boy ... [bsky, 2 points, 0 comments]
- # arXiv The Challenges of Detecting Gases in Exoplanet Atmospheres https:// arxiv.org/abs/2504.21788 for K2-18b, numerous alternative models without potential biosignature gases provide equivalent or [mastodon, 0 points, 0 comments]
- This re-analysis of methods and data casts doubt on the detection of DMS and DMDS biosignatures in the atmosphere of sub-Neptune exoplanet K2-18 b. Great work by @luiswel.bsky.social and team. #astron [bsky, 0 points, 0 comments]
- #arXiv The Challenges of Detecting Gases in Exoplanet Atmospheres https://arxiv.org/abs/2504.21788 for K2-18b, numerous alternative models without potential biosignature gases provide equivalent or be [bsky, 0 points, 0 comments]
- Check out "Interpretation According to Conventional Practices" in our paper and let us know what you think arxiv.org/abs/2504.21788 [bsky, 0 points, 2 comments]
- Reanalysis of the JWST spectrum of K2-18B shows detection is only significant if you assume a specific model. Don’t want to sound glib, but I always tell my students that statistics can’t find somethi [bsky, 0 points, 1 comments]
- Today on the # arXiv : Welbanks et al. 2025, "The Challenges of Detecting Gases in Exoplanet Atmospheres" - https:// arxiv.org/abs/2504.21788 Cool science. Not aliens. [mastodon, 0 points, 0 comments]
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