Kavli Affiliate: Sara Seager
| First 5 Authors: Luis Welbanks, Matthew C. Nixon, Peter McGill, Lana J. Tilke, Lindsey S. Wiser
| Summary:
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.
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