\n<\/p>\n
Astronomers have been on the hunt for a new kind of exoplanet in recent years \u2013 one especially suited for habitability. They\u2019re called hycean worlds, and they\u2019re characterized by vast liquid water oceans and thick hydrogen-rich atmospheres. The name was coined in 2021 by Cambridge astronomer Nikku Madhusudhan, whose team got a close-up look at one possible hycean world, K2-18b, using the James Webb Space Telescope in 2023. In a newly accepted paper this January, Madhusudhan and coauthor Frances Rigby examined what the internal structure of hycean planets might look like, and what that means for the possibility of finding life within.<\/p>\n
<\/p>\n Hycean worlds are unlike anything we have seen in our own solar system, expanding the very definition of a habitable planet. They tend to be much bigger than Earth-like planets, earning them the moniker \u2018mini-neptunes\u2019. Their size makes them easier to detect than smaller rocky worlds, and their thick atmospheres give them a wider habitable zone.<\/p>\n Those same properties also make them ideal candidates for spectroscopic analysis, where measuring the chemical composition of the atmospheres might reveal biosignatures.<\/p>\n In order to tease out the potential characteristics of a habitable hycean world, Rigby and Madhusudhan used a modeling tool called HyRIS to map out possible planetary structures. They limited their models to only allow for habitable temperatures and pressures at the ocean\u2019s surface, where the water meets the air.<\/p>\n Even with those strict conditions in place, the results showed a wide variety of possible internal structures. The ocean depths of a habitable hycean world could range from 10s of kilometers deep to 1000s of kilometers (for comparison, Earth\u2019s ocean averages about 3.7km deep).<\/p>\n One factor that potentially limits the habitability of these worlds is that they are likely to have a thick layer of ice between the ocean floor and the rocky core of the planet. On Earth, the weathering of the rocky seafloor produces nutrients that are essential to life \u2013 ice might inhibit that process. Nonetheless, there is still the possibility that these nutrients could be transported through the ice via convection, or delivered to the planet in other ways, like via comet and asteroid impacts or atmospheric condensation.<\/p>\n The study also looked at several real hycean world candidates, and among them, there are three that stand out as having good chances of habitability. <\/p>\n Although these three candidates orbit red dwarf stars \u2013 known for their violent, hostile solar flares \u2013 these planets\u2019 stars are comparatively calm. They are TOI-270 d, TOI 1468 c, and TOI-732 c (TOI refers to planets observed by the TESS space telescope). <\/p>\n Each of these three planets is scheduled for observation by James Webb in its second year of observing, meaning we\u2019re about to get a more detailed look at some exciting new exoplanets. Last year\u2019s observation of K2-18b was just the beginning of hycean world research, and this recent paper will help astronomers constrain the possible internal structures of these worlds, and help determine the prospect of finding life on them.<\/p>\n Learn More:<\/p>\n Frances E. Rigby, Nikku Madhusudhan, \u201cOn the Ocean Conditions of Hycean Worlds,\u201d ArXiv preprint.<\/p>\n \u201cWebb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18 b.\u201d NASA, September 2023.<\/p>\nLike this:<\/h3>\n