Minimum Radii of Super-Earths: Constraints From Giant Impacts

Many detailed interior structure models of super-Earth planets have been developed. These models show that there is degeneracy in the possible bulk compositions of a super-Earth when the mass and radius are determined via ra-dial velocity and transit measurements, respectively. In addition, the upper and lower envelopes in the mass-radius relationship, currently corresponding to pure ice planets and pure iron planets, respectively, are not physically well-motivated with regards to the physical processes involved in planet formation. Here we apply the results of numerical simulations of giant impacts between super-Earths to constrain the lower bound in the mass-radius diagram that could arise from collisional stripping of a rocky mantle. We find that the current minimum con-straint, that of pure iron super-Earths, is not consistent with mantle stripping under physically reasonable impact conditions. We provide a new estimate for the lower minimum radius boundary for the entire mass range of large terrestrial planets. Subject headings: planets and satellites: formation — planetary systems: forma-tion 1.