Are Hycean exoplanets, which are a combination of hydrogen and a potential liquid water ocean, less common than previously hypothesized? This is what a recent study published in The Astrophysical Journal Letters hopes to address as a team of scientists challenged how characteristics of a recently discovered exoplanet might not hold as advertised. This study has the potential to help scientists better understand the number of Hycean exoplanets, and whether they could be hospitable for life as we know it.
For the study, the researchers used a series of computer models to simulate the formation and evolution of Hycean worlds. The researchers based their study on K2-18b, which is located approximately 124 light-years from Earth and whose April 2025 discovery caused quite a bit of fanfare in the news. The reason is K2-18b was designated as a potential Hycean world that could exhibit a deep liquid water ocean, indicating the possibility of life. Due to their size, which is between Earth and Neptune, astronomers have hypothesized that Hycean worlds could be common throughout the galaxy. However, the simulations proved otherwise.
“In the current study, we analyzed how much water there is in total on these sub-Neptunes,” said Dr. Caroline Dorn, who is an Assistant Professor at the Department of Physics at ETH Zurich and a co-author on the study, “According to the calculations, there are no distant worlds with massive layers of water where water makes up around 50 percent of the planet’s mass, as was previously thought. Hycean worlds with 10-90 percent water are therefore very unlikely.”
This study comes as the number of confirmed exoplanets recently reached 6,000. Therefore, as the number of confirmed exoplanets increases, our understanding of Hycean worlds, and specifically their commonality throughout the galaxy, will increase, too.
What new insights about K2-18b and Hycean worlds will researchers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
Sources: The Astrophysical Journal Letters, EurekAlert!
Featured Image: Artist's illustration of K2-18b. (Credit: ESA/Hubble, M. Kornmesser, CC BY 4.0)
