K2-18b and dimethyl sulfide

The claim

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

Where the idea comes from

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

What the evidence shows

1. 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.
2. The reported signal reached about 3 sigma, short of the 5 sigma physicists usually require for a discovery.
3. Several independent reanalyses found the signal weaker and model-dependent, and other molecules such as ethane or propyne could fit.
4. Some researchers argue the planet may be a gas-rich mini-Neptune with no surface ocean.
5. A 2026 radio search of K2-18b for technosignatures found nothing.

What is still open

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

Our verdict

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

Sources

• Strongest hints yet of biological activity (University of Cambridge)
• New analysis casts doubt (NPR)
• No signs of technology on K2-18b (Astronomy)

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