K2-18b and dimethyl sulfide: aliens or not?

Worth watchingCredible data, genuinely open. The cases that could move the meter.

The claim

"The James Webb telescope found a gas that on Earth only life makes."

A University of Cambridge team led by Nikku Madhusudhan reported dimethyl sulfide (DMS) or dimethyl disulfide in the planet's atmosphere.

K2-18b is about 8.6 times Earth's mass in its star's habitable zone; the team argues it may be a "Hycean" ocean world.
The reported signal reached about 3 sigma, short of the 5 sigma physicists usually require for a discovery.
Several independent reanalyses found the signal weaker and model-dependent, and other molecules such as ethane or propyne could fit.
Some researchers argue the planet may be a gas-rich mini-Neptune with no surface ocean.
A 2026 radio search of K2-18b for technosignatures found nothing.

More Webb observing time and a confirmation by an independent team at high confidence would move this tripwire. Weigh the explanations and vote.

Worth watching The most exciting hint yet, and heavily disputed.

Checked 31 October 2026. Spotted a newer source? Tell us.

Our summary of the main hypotheses, with what supports and what counts against each one.

A statistical fluke in noisy data
For The signal reached about 3 sigma; several independent reanalyses found it weaker or not significant.
Against The team says 16 to 24 more hours of Webb time could push it to 5 sigma, so the question is testable.
A different molecule with a similar fingerprint
For Ethane, propyne and other hydrocarbons can mimic the DMS or DMDS features in the infrared.
Against The original team argues most predicted molecules can't explain the spectrum.
Real DMS, made without life
For DMS has been found on a comet and in interstellar space, so non-living chemistry can make it.
Against Producing the high levels claimed for K2-18b without life is hard to model.
A gas-rich mini-Neptune with no ocean
For Several models fit the planet as a deep, hot gas envelope where life as we know it is unlikely.
Against The "Hycean" ocean model also fits; the data can't yet tell them apart.
Marine life, like plankton on Earth
For On Earth almost all DMS comes from marine microbes. If the signal holds and abiotic routes fail, life is on the table.
Against Needs the signal confirmed at high confidence by another team, plus ruling out the alternatives.

One vote per visitor. Results appear after you vote.

New Webb observations of K2-18b and a confirmation or rejection by an independent team. No new result had been published by October 2026.
Better laboratory data on DMS and DMDS spectra and on non-living sources.
Results on similar "Hycean" candidates such as TOI-270 d.