Composition of 55 Cnc e. Mass-radius relationships for four different rocky compositions: pure iron, super-Mercury (63% iron core above a 37% silicate mantle), Earth-like (33% iron core above a 67% silicate mantle with 10% iron by mol) and a silicate planet with no iron. The green band depicts the range of rocky compositions of planets between 1 and 30 M _⊕ . Two families of volatile planets are considered: envelopes of H-He with 0.01, 0.1 and 1% by mass (pink) and envelopes of water with 20, 50% water. Kepler-10b (K-10b) and CoRoT-7b (C-7b) are shown for reference. Data for 55 Cnc e from this study are shown in red, and are taken from D11 (1) and W11 (2).