Compositions and interior structures of planets TRAPPIST-1b through e. Panel A: representative possible interior structures of planets b through e, with layers of liquid water (dark blue), high-pressure ice polymorphs(light blue), rock (brown), and iron (black). Planets d and e are far enough from the TRAPPIST-1 star topotentially have a layer of solid ice (white) on their surfaces. Panels B–E: compositions of planets b through e, where the colour-coding indicates the volume fraction of H₂ O permitted in each planet (ϕ_H2O = ϕ_iw + ϕ_hpp) as a functionof its volume fraction of iron (ϕ_Fe) and rock (ϕ_r). Black stars indicate the cases shown in panel A. Planets b and d are substantially more H₂ O-rich than planets c and e.