James Webb Telescope may detect alien life on 'Hycean' planets
23 Mar 2025

The James Webb Space Telescope (JWST) could detect signs of life on a class of exoplanets called "hycean" worlds.

These planets have deep oceans and a thick hydrogen atmosphere, which could give clearer biosignature signals than Earth-like planets.

Astrobiologist Eddie Schwieterman from the University of California, Riverside says that "hycean planets offer a much clearer signal."

What are Hycean worlds?
Exoplanets

Hycean worlds, a term coined by planetary scientist Nikku Madhusudhan in 2021, remain hypothetical. They are thought to orbit red dwarf stars.

K2-18b, a "sub-Neptune" world 124 light-years away from Earth in the constellation Leo, is a potential candidate for such a planet.

The Hubble Space Telescope found water vapor in its atmosphere in 2019 and JWST has detected carbon dioxide and methane there too.

Methyl halides could be key to detecting life
Biosignature

A team of researchers from the University of California, Riverside and ETH Zurich in Switzerland suggest that methyl halides, compounds produced by microbial ocean life on Earth, could serve as a biosignature on hycean worlds.

"Methyl halides on hycean worlds offer a unique opportunity for detection with existing technology," said Michaela Leung from UC Riverside.

These molecules include carbon and three hydrogen atoms attached to a halogen atom like bromine or chlorine.

Conditions on Hycean worlds may favor methyl halides
Detection

Leung's team speculates that conditions on hycean worlds (if they exist) could allow methyl halides to build up in the atmosphere in large quantities.

Additionally, these compounds would have strong absorption features in infrared light at the same wavelengths JWST is designed to observe.

"One of the great benefits of looking for methyl halides is you could potentially find them in as few as 13 hours with James Webb," Leung explained.

Challenges remain in detecting life on Hycean worlds
Obstacles

Despite their potential, detecting life on hycean worlds comes with challenges. It's still unclear whether these planets actually exist or if their oceans could support life.

The conditions beneath the hydrogen envelope may be too hot for known forms of life, but if methyl halides were detected there, it would suggest life could exist in a deep ocean.

"These microbes, if we found them, would be anaerobic," Schwieterman said.