K2-18b Does Not Meet The Standards Of Evidence For Life

K2-18b, a temperate sub-Neptune, has garnered important consideration as a result of claims of doable biosignatures in its environment. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked appreciable debate, primarily round arguments that their absorption options aren’t uniquely identifiable.

Here, we think about a unique query from the astrobiology requirements of proof framework: Have we detected an genuine sign? To reply this, we analyzed previously-published, publicly-available JWST observations of K2-18b utilizing impartial knowledge discount and spectral retrieval frameworks.

Our complete set of reductions demonstrates that the MIRI transit spectrum is extremely prone to unresolved instrumental systematics. Applying completely different wavelength binning schemes yields a potpourri of planet spectra that then result in a large assortment of atmospheric interpretations. Consequently, we provide suggestions to assist decrease this previously-underappreciated instrument systematic in future MIRI reductions of any exoplanet.

While the MIRI binning scheme adopted by Madhusudhan et al. (2025) helps a tentative detection of DMS/DMDS in K2-18b, we discover that 87.5% of retrievals utilizing our favored MIRI binning scheme don’t. When contemplating the complete, 0.7 – 12 micron transit spectrum, we affirm the detection of CH₄ and CO₂, and discover the presence of DMS and C₂H₄ to be interchangeable.

Moreover, we discover that the tentative presence of huge options within the MIRI transit spectrum is in stress with the extra strong, but smaller, options noticed within the close to IR. We conclude that purple noise — reasonably than an astrophysical sign — plagues the mid-IR knowledge and there’s, as but, no statistically important proof for biosignatures within the environment of K2-18b.

Kevin B. Stevenson, Jacob Lustig-Yaeger, E. M. May, Ravi Ok. Kopparapu, Thomas J. Fauchez, Jacob Haqq-Misra, Mary Anne Limbach, Edward W. Schwieterman, Kristin S. Sotzen, Shang-Min Tsai

Comments: Submitted to AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2508.05961 [astro-ph.EP] (or arXiv:2508.05961v1 [astro-ph.EP] for this model)
https://doi.org/10.48550/arXiv.2508.05961
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Submission historical past
From: Kevin Stevenson
[v1] Fri, 8 Aug 2025 02:49:13 UTC (2,514 KB)

Astrobiology,