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Title: Does the atmosphere of K2-18 b contain dimethyl sulfide?
Plain: A team using JWST reported hints of dimethyl sulfide, a gas made on Earth almost only by marine life, on the planet K2-18 b. Other teams analyzing the same data find no reliable signal.
Precise: K2-18 b is a temperate sub-Neptune ($R \sim 2.6 R_{\mathrm{earth}}, M \sim 9 M_{\mathrm{earth}}$) orbiting an M dwarf, with CH4 and CO2 detected by JWST in 2023. Determine whether dimethyl sulfide (and dimethyl disulfide) is present at $\ge 5\sigma$ in JWST NIRISS, NIRSpec and MIRI spectra, and if present, whether abiotic photochemistry or delivery can produce the inferred abundance.
Settled by: Additional JWST transits analyzed by independent pipelines with agreed systematics treatment, reaching a $5\sigma$ detection or an upper limit below the claimed abundance.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: A 2025 MIRI analysis reported about $3\sigma$ evidence for dimethyl sulfide or dimethyl disulfide; independent 2025 reanalyses found no statistically significant evidence, and 2026 papers model the spectrum without dimethyl sulfide.
Posed since: 2023