The Distribution of Impactor Core Material During Large Impacts on Earth-like Planets

Large impacts onto young rocky planets may transform their compositions,creating highly reducing conditions at their surfaces and reintroducing highlysiderophile metals to their mantles. Key to these processes is the availabilityof an impactor's chemically reduced core material (metallic iron). It is,therefore, important to constrain how much of an impactor's core remainsaccessible to a planet's mantle/surface, how much is sequestered to its core,and how much escapes. Here, we present 3D simulations of such impact scenariosusing the shock physics code iSALE to determine the fate of impactor iron.iSALE's inclusion of material strength is vital in capturing the behavior ofboth solid and fluid components of the planet and thus characterizing ironsequestration to the core. We find that the mass fractions of impactor corematerial that accretes to the planet core (f_core) or escapes (f_esc)can be readily parameterized as a function of a modified specific impactenergy, with f_core > f_esc for a wide set of impacts. These resultsdiffer from previous works that do not incorporate material strength. Our workshows that large impacts can place substantial reducing impactor core materialin the mantles of young rocky planets. Impact-generated reducing atmospheresmay thus be common for such worlds. However, through escape and sequestrationto a planet's core, large fractions of an impactor's core can be geochemicallyhidden from a planet's mantle. Consequently, geochemical estimates of latebombardments of planets based on mantle siderophile element abundances may beunderestimates.