The influence of recent major crater impacts on the surrounding surfaces of (21) Lutetia

Abstract

We present 3-D simulations of impacts into Asteroid 21 Lutetia, the subject of a fly-by by the European Space Agency’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko. Using a 3-D shape model of the asteroid, impacts of sizes sufficient to reproduce the observed craters in Lutetia’s North Polar Crater Cluster (NPCC) as observed by the OSIRIS experiment have been simulated using the Smoothed Particle Hydrodynamics technique. The asteroid itself has been modelled both as a homogeneous body and as a body with an iron core. Crater erasure in the vicinity of the NPCC has been observed by OSIRIS. The results show that this erasure has most probably been caused by ejecta deposition following the impact of a 2.3 km diameter projectile impacting at a velocity of 5 km s1 (or an impact with similar energy). This would produce a crater of roughly 34 km in diameter comparable to the largest (and oldest) member of the NPCC. Erasure of craters via the shock associated with such an impact is shown to be less significant and does not reproduce the observed spatial distribution of erased craters or ‘‘ghost’’ craters. Time series of the surface velocity fields resulting from the simulated impacts are also presented. It is suggested that the surface velocity field and velocity shear may play a role in the generation of lineaments. Our model calculations show that the velocity field lines around 50 s after impact exhibit a reasonable qualitative correlation with the orientation of lineaments observed on the entire visible surface of Lutetia. It is also shown that incorporation of a core of 25–30 km in diameter does not modify the velocity field evolution with time and, as such, the presence or otherwise of such a core cannot be inferred from lineament observations if this concept for their formation is valid.