Context: 

For the First time, a team of astronomers at University of Cambridge, using NASA’s James Webb Space Telescope (JWST), have detected chemical traces in the atmosphere of a distant exoplanet K2-18b.

Key findings

Sulphur-Containing Molecules: The research team found compelling evidence for the presence of two sulphur-containing molecules in the atmosphere of K2-18b:

• Dimethyl sulphide (DMS)
• Dimethyl disulphide (DMDS)
• On Earth, both of these compounds are byproducts of biological processes, particularly from marine microorganisms. 
• This has led to scientists hypothesising on the possibility of a warm ocean on K2-18b, an environment similar to the one that gave rise to life on Earth about 3.5 to 4 billion years ago. 

Molecule Degradation: These molecules degrade rapidly in the atmosphere unless replenished by life. The unexpectedly high concentrations of these molecules on K2-18b are difficult to explain through non-biological processes alone.

Previous Observations: In 2023, JWST had already detected methane and carbon dioxide in the planet’s atmosphere, both consistent with life-supporting conditions, and hinted at the presence of DMS. 

• In 2019, data from the Hubble Telescope had detected signals of the presence of water vapour in K2-18b’s atmosphere. 

Use of MIRI: The new study, using JWST’s Mid-Infrared Instrument (MIRI) operating in a different wavelength range, confirms those suspicions with a “strong and clear” signal for either DMS, DMDS, or both.

Transit Method: The team used the technique of observing a transit, where K2-18b passes in front of its star, dimming the starlight. This allowed JWST to analyze the planet’s atmosphere by detecting changes in the star's light caused by the gases present.