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 Universite/CNES)[1] 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.

These findings, recently published in The Astrophysical Journal Letters, show that mini-Neptunes could be super-Earths with a rocky core surrounded by water in a supercritical state[2], suggesting that these two types of exoplanet may form in the same way.

Another paper recently published in Astronomy and Astrophysics, involving in France scientists mainly from the CNRS and the University of Bordeaux[3], focused on the effect of stellar irradiation on the radius of Earth-sized planets containing water.

Their work shows that the size of the atmospheres of such planets increases considerably when subject to a strong greenhouse effect, in line with the study on mini-Neptunes.

Future observations should make it possible to test these novel hypotheses put forward by French scientists, who are making major contributions to our knowledge of exoplanets.

Research Reports: "Irradiated Ocean Planets Bridge Super-Earth and Sub-Neptune Populations" and "Revised Mass-Radius Relationships for Water-Rich Rocky Planets More Irradiated Than the Runaway Greenhouse Limit"

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Supercomputer reveals atmospheric impact of gigantic planetary collisions
Durham UK (SPX) Jul 15, 2020
The giant impacts that dominate late stages of planet formation have a wide range of consequences for young planets and their atmospheres, according to new research. Research led by Durham University and involving the University of Glasgow, both UK, has developed a way of revealing the scale of atmosphere loss during planetary collisions based on 3D supercomputer simulations. The simulations show how Earth-like planets with thin atmospheres might have evolved in an early solar system dependi ... read more