University ETH ZurichThere is much less water on the surfaces of distant planets outside our solar system than previously thought, according to new research. “Water on planets is much more limited than previously believed,” notes Caroline Dorn, professor of exoplanets at ETH Zurich. “The water that actually remains on the surface as H2O is limited to a few per cent at most.”In an earlier publication, Dorn’s group was already able to show how most of a planet’s water is hidden in the interior. “In the current study, we analyzed how much water there is in total on these sub-Neptunes,” explains the researcher, “According to the calculations, there are no distant worlds with massive layers of water where water makes up around 50% of the planet’s mass, as was previously thought. Instead, they highlight the dominant role of the equilibrium between magma ocean and atmosphere in shaping planetary composition,” concludes Werlen.