New Constraints On DMS and DMDS In The Atmosphere Of K2-18 b From JWST MIRI
The sub-Neptune frontier has opened a new window into the rich diversity of planetary environments beyond the solar system.
The possibility of hycean worlds, with planet-wide oceans and H2-rich atmospheres, significantly expands and accelerates the search for habitable environments elsewhere.
Recent JWST transmission spectroscopy of the candidate hycean world K2-18 b in the near-infrared led to the first detections of carbon-bearing molecules CH4 and CO2 in its atmosphere, with a composition consistent with predictions for hycean conditions.
The observations also provided a tentative hint of dimethyl sulfide (DMS), a possible biosignature gas, but the inference was of low statistical significance.
We report a mid-infrared transmission spectrum of K2-18 b obtained using the JWST MIRI LRS instrument in the ~6-12 μm range. The spectrum shows distinct features and is inconsistent with a featureless spectrum at 3.4-σ significance compared to our canonical model. We find that the spectrum cannot be explained by most molecules predicted for K2-18 b with the exception of DMS and dimethyl disulfide (DMDS), also a potential biosignature gas.
We report new independent evidence for DMS and/or DMDS in the atmosphere at 3-σ significance, with high abundance (≳10 ppmv) of at least one of the two molecules. More observations are needed to increase the robustness of the findings and resolve the degeneracy between DMS and DMDS.
The results also highlight the need for additional experimental and theoretical work to determine accurate cross sections of important biosignature gases and identify potential abiotic sources. We discuss the implications of the present findings for the possibility of biological activity on K2-18 b.
Spectral contributions of notable chemical species in the MIRI band. Each curve denotes the spectral contribution of a particular molecule to the model spectrum, as denoted in the legend. The mixing ratios of DMS and DMDS are set to a representative value of 5 × 10−4 , while CH4 and CO2 are set to 10−2 , consistent with constraints obtained from previous near-infrared observations (Madhusudhan et al. 2023b). The black line denotes the resulting transmission spectrum with all molecular contributions combined. The individual spectral contributions of these molecules are shown in Figure 3. — astro-ph.EP
Nikku Madhusudhan, Savvas Constantinou, Måns Holmberg, Subhajit Sarkar, Anjali A. A. Piette, Julianne I. Moses
Comments: Accepted for publication in ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2504.12267 [astro-ph.EP] (or arXiv:2504.12267v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.12267
Focus to learn more
Submission history
From: Madhusudhan Nikku
[v1] Wed, 16 Apr 2025 17:28:53 UTC (15,551 KB)
https://arxiv.org/abs/2504.12267
Astrobiology, Astrochemistry, Exoplanet,
