The influence of interior structure and thermal state on impact melt generation during the early evolution of planetesimals and terrestrial planets

Kurzfassung

Impact cratering events and collisions of large bodies are a fundamental process during the formation of the solar system and result in the generation of huge quantities of impact-induced melt that affects the further evolution and appearance of the target body. Traditionally, melt quantities are estimated by semi-analytical models or parameterized results from hydrocode simulations that calculate impact-induced melt. These so-called scaling laws roughly estimate the melt volume using basic impactor and target properties, which are assumed constant. The latter is valid for homogenous targets which usually applies for relatively small impact events, but it becomes more problematic if the impact significantly affects deeper target regions where target properties substantially change. Furthermore, previous studies indicate that plastic work and decompression melting can significantly contribute to the total melt production, which is usually not considered by scaling laws. We aim at developing more accurate melt predictions that include a comprehensive representation of target and projectile interdependencies during large collisions throughout the history of the solar system. To this end, we run numerical models of impact events using the iSALE shock physics code, which we have extended with a massless Lagrangian tracer-based method to account for the target's thermal profile, decompression melting and plastic work. As a general representation of bodies that exist or have existed in the solar system, we consider a set of generic models of terrestrial planets and planetesimals. For these target bodies we calculate the radial thermal structure by employing parameterized thermal evolution models that account for partial melting of the mantle and crustal growth. The resulting interior structure of the target body at different times and evolution stages is then used as the initial condition for the impact simulations.