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Characterisation of the interior structures and atmospheres of multiplanetary systems

Acuña, Lorena; Lopez, Theo; Morel, Thierry; Deleuil, Magali; Mousis, Olivier; Aguichine, Artem; Marcq, Emmanuel; Santerne, Alexandre

The increasing number of well characterised low-mass planets, combined with the valuable informations from stellar and planetary spectroscopy, opens the way to the modeling of planetary structures and compositions, which can be obtained with theoretical and numerical works. This approach gives a valuable insight to understand the formation of planetary systems in the low-mass range. We present a 1D planetary model where the interior is coupled with the atmosphere in radiative-convective equilibirum within a Bayesian retrieval scheme. In addition to a Fe core and a silicate mantle, we take into account water in all its possible phases, including steam and supercritical phases, which is necessary for systems with a wide range of stellar irradiations.

Our interior-atmosphere model calculates the compositional and atmospheric parameters, such as Fe and water content, surface pressures, scale heights and albedos. We analyse five multiplanetary systems: K2-138, TOI-178, Kepler-11, Kepler-102 and Kepler-80. From the individual composition of their planets, we derive a similar trend for these systems: a global increase on the water content with increasing distance from the star in the inner region of the systems, while the planets in the outer region present a constant water mass fraction. This trend reveals the possible effects of migration type, formation in the vicinity of the ice line and XUV atmospheric mass loss during their formation history. Slight deviations from this trend can be explained case by case with H/He atmospheres, Jeans atmospheric escape and high-CMF processes, such as mantle evaporation or formation in the vicinity of rocklines.

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