These giant, ocean worlds are likely to be significantly more abundant than Earth-like exoplanets.
In the search for potentially habitable worlds, astronomers have focused on Earth-like planets orbiting Sun-like stars. These rocky worlds have a similar radius and mass to Earth and must be warm enough to allow liquid water to exist on the surface.
These new candidates are ocean worlds significantly larger than Earth but smaller than Neptune and enveloped in a hydrogen-rich atmosphere. Crucially, they must have a temperature at their surface that allows liquid water to flow, so in this respect they are like Earth.Madhusudhan and colleagues call these worlds "Hycean", a portmanteau from the words hydrogen and ocean. They say these worlds can have a radius up to 2.6 that of Earth’s and be up to ten times as massive.
Another reason for the much broader zone is that “cold” Hycean worlds could support liquid water by virtue of their internal heating. Such planets would require little or no radiation from the parent star and so could orbit at vast distances. “Our results show that the [habitable zone] for Hycean planets is considerably wider than the terrestrial [habitable zone],” they say.Should these planets support life, an important question is whether they would display measurable biosignatures.
France Dernières Nouvelles, France Actualités
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