less Water on Distant planets Than Previously thought

There is much less water on the surfaces of distant planets outside our solar system than previously thought, according to new research.

These exoplanets do not have thick layers of water, as was often speculated, the researchers report.

An exoplanet orbiting a dwarf star 124 light-years from Earth made headlines around the world in April 2025. Researchers at the University of Cambridge reported that planet K2-18b could be a marine world with a deep, global ocean teeming with life.

however, the new study now shows that so-called SUB-Neptunes such as K2-18b are highly unlikely to be worlds dominated by water and that conditions there are far from conducive to life.

“Water on planets is much more limited than previously believed,” notes Caroline Dorn, professor of exoplanets at ETH Zurich.

The study was conducted under the leadership of ETH Zurich, in collaboration with researchers from the Max Planck Institute for Astronomy in Heidelberg and the university of California in Los Angeles.

K2-18b is larger than Earth but smaller than neptune,placing it in a class of planets that do not exist in our solar system. however,observations show that they are common in outer space. Some of these sub-Neptunes were probably formed far away from their central star, beyond the so-called snow line where water freezes into ice and later migrates inwards.

Until now,it had been assumed that some of these planets were able to accumulate especially large amounts of water during their formation and now harbor deep,global oceans beneath a hydrogen-rich atmosphere. Experts refer to these as Hycean planets: a combination of “hydrogen” and “ocean”.

“Our calculations show that this scenario is not possible,” says Dorn. This is because a fundamental vulnerability of previous studies was that they ignored any chemical coupling between the atmosphere and the interior of the planet.

“We have now factored in the inter