Many exoplanets known today are ‘super-Earths,’ with a radius 1.3 times that of Earth, and ‘mini-Neptunes,’ with 2.4 Earth radii. Mini-Neptunes, which are less dense, were long thought to be gas planets, made up of hydrogen and helium. Now, scientists at the Laboratoire d’Astrophysique de Marseille (CNRS/Aix-Marseille Université/Cnes) have examined a new possibility, namely that the low density of mini-Neptunes could be explained simply by the presence of a thick layer of water that experiences an intense greenhouse effect caused by the irradiation from their host star.
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Source: Phys.org