Impactor Core Fragmentation During Impacts in the Late Accretion Phase

The influence of asteroid impacts during the late accretion phase on Earth’s present day composition is still not fully understood. One important question here is if the mixing of metal cores from differentiated impactors into an existing magma ocean could explain the relatively high concentrations of highly siderophile elements observed in Earth’s mantle. For this it is essential to know how much the impactor cores break apart during the impact process, since a more fragmented body will allow more mixing with the surrounding material.

We simulate the impacts of differentiated impactors into magma oceans using the grid-based Eulerian shock physics code iSALE. We developed and implemented a new method to improve the fragmentation behavior in such Eulerian codes and used it to study the fragmentation and dispersion of the metal core of the differentiated impactor. We vary the size and velocity of the impactor as well as target properties like the depth of the magma ocean and its viscosity.

We see significant fragmentation of the impactor core under most tested parameters. Higher impact velocity and greater magma ocean depth show an especially pronounced increase in core fragmentation.

Acknowledgments: We gratefully acknowledge the developers of iSALE-2D, including Gareth Collins, Kai Wünnemann, Dirk Elbeshausen, Tom Davison, Boris Ivanov and Jay Melosh. This work was funded by the Deutsche Forschungsgemeinschaft (SFB-TRR170, subproject C2 and C4).