The Challenges of Detecting Gases in Exoplanet Atmospheres
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.
We illustrate these challenges using the sub-Neptune K2-18~b, where recent claims of a potential biosignature detection vanish when the considered model space is expanded. We show that numerous alternative models without potential biosignature gases provide equivalent or better fits to the observations.
We demonstrate that the significance of a claimed detection relies on the choice of models being compared, and that model preference does not necessarily imply the presence of any specific gas.
Luis Welbanks, Matthew C. Nixon, Peter McGill, Lana J. Tilke, Lindsey S. Wiser, Yoav Rotman, Sagnick Mukherjee, Adina Feinstein, Michael R. Line, Sara Seager, Thomas G. Beatty, Darryl Z. Seligman, Vivien Parmentier, David Sing
Comments: Submitted for peer review
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2504.21788 [astro-ph.EP] (or arXiv:2504.21788v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.21788
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Submission history
From: Luis Welbanks
[v1] Wed, 30 Apr 2025 16:47:28 UTC (1,993 KB)
https://arxiv.org/abs/2504.21788
Astrobiology
