Hycean planets, theoretical exoplanets with deep oceans and thick hydrogen atmospheres, could be key targets for detecting biosignatures. A new study suggests these planets provide clearer signals of potential life than Earth-like worlds.
Researchers propose that methyl halides, chemical compounds produced by microbial life in Earth’s oceans, could serve as a detectable biosignature in the atmospheres of hycean planets. These molecules may accumulate in large quantities under suitable conditions.
Unlike oxygen, which is difficult to detect on Earth-like exoplanets, methyl halides produce strong infrared absorption features. The James Webb Space Telescope (JWST) is well-equipped to identify these markers in a relatively short observation period.
K2-18b, a sub-Neptune exoplanet 124 light-years away, is considered a strong candidate for a hycean world. Previous observations from the Hubble and James Webb telescopes have detected water vapour, carbon dioxide, and methane in its atmosphere.
The existence of hycean planets remains hypothetical, and confirming liquid oceans beneath their hydrogen atmospheres is not yet feasible. Additionally, their extreme temperatures raise uncertainties about whether they could sustain life.
If life exists on a hycean world, it would likely be anaerobic, meaning it does not rely on oxygen. On Earth, some microbes survive without oxygen, suggesting that similar life forms could exist in these environments.
Hycean worlds may be more resilient to radiation from red dwarf stars than Earth-like planets, making them better candidates for hosting life. Given that red dwarfs are the most common stars in the Milky Way, habitable hycean planets could be widespread.