Magma oceans on volatile-rich exoplanets: from ultra hot super-Earths to temperate sub-Neptunes

Constraining the interior of exoplanets is a very degenerated problem with many solutions. A very promising possibility is the spectroscopic study of planets for which the atmosphere is chemically exchanging with the molten planet's mantle: these are planets with a magma ocean. Rocky exoplanets with a magma ocean at their surface are those with equilibrium temperature temperature > 1400 K. They are a new category of planets that still need to be characterized and the unambiguous detection of a magma ocean is still elusive. I will discuss about the atmosphere of magma ocean exoplanets, and in particular the effect of hydrogen and volatiles (water, CO2) and show spectral signatures when a magma ocean is in contact with the atmosphere. I will extend the discussion to sub-Neptunes, with equilibrium temperatures < 1000 K , and show that they can have a magma ocean hidden under a thick atmospheric layer that may be an explanation to the high metallicities observed in some of sub-Neptunes. I will also discuss possibilities to constrain magma-ocean compositions on sub-Neptunes.