Many exoplanets known today are either super-Earths with a radius of 1.3 times the Earth’s radius, or mini-Neptune with 2.4 Earth radii. Mini-neptunes, which have always been less dense, have long been thought of as gaseous planets composed of hydrogen and helium. Now scientists from the Marseille Astrophysics Laboratory have explored the new possibility and presented their research in the Astrophysical Journal Letters.
Astrophysicists have suggested that the low density of mini-neptune-type planets can be explained simply by the presence of a thick layer of water, which is subject to an intense greenhouse effect.
Where does the greenhouse effect come from on these exoplanets? It is caused by radiation from a star whose radiation the planet is exposed to.
These results indicate that mini-neptuns may be super-Earths with a rocky core surrounded by supercritical water. Water takes on this state at very high pressures and temperatures. This study also suggests that two types of exoplanets – super-earths and mini-neptune – can form in the same way.
Another study, recently published in Astronomy & Astrophysics, looked at the effect of stellar radiation on the radius of Earth-sized planets containing water. French scientists from the Bordeaux Astrophysics Laboratory used a model of the planet’s atmosphere developed at the Laboratory of Dynamic Meteorology in their study.
Their results show that the size of the atmospheres of such planets increases significantly when they are exposed to a strong greenhouse effect, in accordance with studies of planets such as mini-neptune. Future observations should allow us to test these new hypotheses put forward by French scientists who are contributing to our knowledge of exoplanets.