Hycean worlds, a new class of exoplanets, have recently come into focus as promising candidates in the search for extraterrestrial life. Marked by their deep oceans and extensive hydrogen atmospheres, these planets are hypothesized to orbit red dwarf stars. The exoplanet K2-18b has recently been touted as the best candidate so far for a hycean world. Located 124 light-years away in the constellation Leo, K2-18b is a sub-Neptune-sized exoplanet that orbits in the habitable zone of its star. In 2019, the Hubble Space Telescope performed a historic observation – the first definitive detection of water vapor in the atmosphere. As of now, recent observations from the JWST have indeed detected carbon dioxide and methane, giving much stronger support for the hycean hypothesis.
Detecting these gases in K2-18b’s atmosphere would be a clear confirmation of the hycean planet hypothesis’s predictions. This hypothesis posits that such worlds may produce just the right conditions for detecting biosignatures. Methyl halides are pollutants that microbial life could be creating in our oceans. Due to the strongly reducing conditions, these compounds will most likely accumulate in the atmospheres of hycean worlds. These compounds produce very distinct absorption signatures in infrared light. With its unprecedented capabilities at these wavelengths, the JWST is turning out to be a powerful tool for identifying signs of life.
“Unlike an Earth-like planet, where atmospheric noise and telescope limitations make it difficult to detect biosignatures, hycean planets offer a much clearer signal,” – Eddie Schwieterman
Hycean, a new word combining hydrogen and ocean, refers to a hypothetical ocean world with abundant ecosystems. This possibility was first introduced by planetary scientist Nikku Madhusudhan from the University of Cambridge in 2021. Hycean planets have a lot of potential but their physical existence is still theoretical. Yet, their thick hydrogen atmospheres might offer shielding from stellar activity, potentially allowing these worlds to host a stable environment conducive to life.
As such, the JWST’s recent discoveries have lent credence to the idea that hycean worlds may be excellent targets for future biosignature detection. Carbon dioxide and methane are seen, but not carbon monoxide and ammonia. This would be consistent with the expected atmospheric composition of a hycean world. Such observations are a wonderful step forward in our understanding of these weird and wonderful exoplanets.
“However, methyl halides on hycean worlds offer a unique opportunity for detection with existing technology.” – Michaela Leung
With the possibility of methyl halides being detectable, there’s an exciting prospect for astronomers to seek whatever life may lie beyond. These compounds can still be observed with fairly brief—not decades—of follow-up time within reach of the JWST.
“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. That is similar or lower, by a lot, to how much telescope time you’d need to find gases like oxygen or methane,” – Michaela Leung
Methyl halides are simpler to detect. Most importantly, they provide clear biosignatures of potential microbial life, which would by nature be anaerobic in nature.
“These microbes, if we found them, would be anaerobic,” – Eddie Schwieterman
The Astrophysical Journal Letters recently published new research on hycean worlds. NASA via Unsplash The research uncovers thrilling new evidence about their likely habitability. As scientists continue to explore these distant worlds, they may uncover evidence that could redefine our understanding of life beyond Earth.
