I’m sure we’ve all seen the reports on this planet in the last week. K2-18b is a world about nine times as massive as earth about 120 light years away. JWST has found biosignature gases DMS and/or DMDS in its atmosphere with NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments, confirming a discovery made with its Mid-Infrared Instrument (MIRI) previously.

“The signal came through strong and clear.”

Based on its size and other characteristics, astronomers suspect that K2-18b may be a “Hycean” world — a class of exoplanet proposed in 2021 that has a huge liquid-water ocean and a hydrogen-rich atmosphere. (“Hycean” is a portmanteau of “hydrogen” and “ocean.”)

And K2-18b’s air is also rich in DMS and/or DMDS, according to the new study. The researchers estimate concentrations of more than 10 parts per million by volume, compared to less than one part per billion for them here on Earth.

“Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds,” Madhusudhan said. “And now we’ve observed it, in line with what was predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have.”