Hycean worlds, a type of exoplanet with deep oceans and thick hydrogen atmospheres, may provide the best chance for the James Webb Space Telescope (JWST) to detect signs of life. According to a new study, these planets offer clearer biosignature signals than Earth-like planets due to reduced atmospheric noise.
The name “Hycean” is derived from “hydrogen” and “ocean,” a term first introduced in 2021 by planetary scientist Nikku Madhusudhan. While their existence remains hypothetical, astronomers believe these planets could be promising targets for studying alien life.
Scientists are particularly interested in detecting methyl halides, a group of chemicals produced by certain bacteria and ocean algae on Earth. These molecules, containing carbon, hydrogen, and halogen atoms, could serve as strong biosignatures in Hycean atmospheres.
Unlike oxygen, which is difficult to detect on Earth-like exoplanets, methyl halides are more easily identifiable due to their distinct infrared absorption features. JWST is well-equipped to observe these molecules, offering a promising method for identifying potential life.
K2-18b: A Promising Hycean World with Detectable Biosignatures Using JWST
One of the best candidates for a Hycean world is K2-18b, a “sub-Neptune” exoplanet orbiting in the habitable zone of a red dwarf star 124 light-years away. Observations from the Hubble Space Telescope in 2019 confirmed the presence of water vapor in its atmosphere. More recently, JWST has detected carbon dioxide, methane, and possible traces of dimethyl sulfide—a compound produced by ocean plankton on Earth. If confirmed, these findings could strengthen the case for life on Hycean planets.
Researchers from the University of California, Riverside, and ETH Zurich suggest that detecting methyl halides on Hycean worlds may be significantly easier than finding oxygen on Earth-like exoplanets. These molecules could accumulate in high concentrations in a hydrogen-rich atmosphere, making them strong biosignature candidates. Moreover, JWST could potentially detect them within just 13 hours of observation, making it a cost-effective method compared to searching for gases like oxygen or methane.
Challenges in Confirming Life on Hycean Worlds
Despite their potential, two major challenges remain. First, the existence of Hycean planets is still unconfirmed, as they have only been proposed based on theoretical models. Second, the habitability of their deep oceans is uncertain. While the thick hydrogen atmosphere may keep the ocean from evaporating, conditions could be too extreme for life as we know it. However, if methyl halides are found, it would provide strong evidence that microbial life could thrive in such environments.
If life exists on Hycean worlds, it would likely be anaerobic, meaning it would rely on hydrogen rather than oxygen. Such lifeforms would resemble certain microbes on Earth that survive without oxygen. Red dwarf stars, which make up about 75% of all stars in the Milky Way, often emit strong radiation that can strip atmospheres from Earth-like planets.
However, Hycean worlds, with their thick atmospheres, may be more resilient. If this is the case, these planets could outnumber Earth-like habitable worlds, making them prime targets in the search for extraterrestrial life.
