Scientists Dispute 3-Sigma DMS Signal on K2-18b as Webb Reanalyses Find No Clear Detection
Updated
Updated · spacedaily.com · Jul 10
Scientists Dispute 3-Sigma DMS Signal on K2-18b as Webb Reanalyses Find No Clear Detection
3 articles · Updated · spacedaily.com · Jul 10
Summary
Several independent teams reanalyzing James Webb data say K2-18b’s reported dimethyl sulfide signal is not statistically strong enough to count as a detection, challenging a high-profile biosignature claim.
The dispute centers on a roughly 3-sigma result reported in 2025 by a Cambridge-led team, with critics finding the mid-infrared spectrum could be nearly flat or explained equally well by other gases.
NASA-led and journal-published follow-up studies also found insufficient evidence for DMS or dimethyl disulfide, even as some analyses still support water vapor, methane and carbon dioxide in the planet’s atmosphere.
The uncertainty runs deeper than one molecule: K2-18b, 124 light-years away and about 8.6 Earth masses, may be a hycean ocean world or a gas-rich mini-Neptune with no habitable surface.
For now, researchers say only more Webb observations and shared detection standards can show whether DMS is really present—let alone whether it would mean life.