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Fig. 3


Example of a scenario for TRAPPIST-1 planets where masses and radii follow an interior isocomposition line (gray line; 10% Fe, 90% MgSiO3 composition) chosen to be consistent with 2σ uncertainty ellipses of Grimm et al. (2018). While the seven large ellipses indicate the known current estimates (95% confidence) for the masses and radii of the seven TRAPPIST-1 planets, the seven small circles indicate the positions (in the mass, radius diagram) of the seven planets as speculated in our scenario. Each planet (associated with a current uncertainty ellipse, and a speculated position) is identified by a distinct color. This figure also shows mass-radius relationships for terrestrial core planets, in some cases endowed with either a condensed layer of water (solid blue line) or a steam H2O atmosphere of various masses (dashed purple lines). The mass-radius relationships for steam planets can be built following the procedure described in Appendix D. We note that the mass-radius relationships for steam H2O-rich atmosphere planets can slightly change depending on the level of stellar irradiation they receive. However, because these changes are low (for the levels of irradiation on TRAPPIST-1 b, c, and d) compared to the runaway-greenhouse-transition-induced mass-radius relationship change, we decided no to show them for clarity.

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