There might be a type of exoplanet without dry land. They're called "Hycean" worlds, a portmanteau of "hydrogen" and "ocean." They're mostly or entirely covered in oceans and have thick hydrogen atmospheres.
They're intriguing because their atmospheres keep them warm enough to have liquid water outside of the traditional habitable zones. If they do exist, scientists think they're good candidates to support microbial life.
Hycean worlds are hypothetical, but there is some evidence that they exist. The Kepler mission detected many candidates and provided foundational evidence for their existence. However, it didn't detect any with certainty.
More recently, JWST observations also supported the idea. The space telescope detected carbon dioxide and methane in the atmosphere of a candidate Hycean world called K2-18b. Both of those molecules can be biosignatures of microbial life under similar conditions as Earth's oceans.
New research published in the Monthly Notices of the Royal Astronomical Society examines the potential Hycean worlds hold for the evolution of life and how life might depend on these worlds' thermodynamic conditions. It's titled "Prospects for Biological Evolution on Hycean Worlds." The authors are Emily G Mitchell and Nikku Madhusudhan, both from the University of Cambridge.
"The search for extraterrestrial life is one of the most fundamental quests in human history," the authors write. "An important recent development in this direction is the possibility of Hycean worlds, which increase both the numbers of potentially habitable planets and the ability to detect biosignatures in their atmospheres."
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