Simulation of the formation of a large crater on Lutetia
This image shows a series of snapshots obtained from computer simulations designed to study the formation of craters due to the impact of a smaller body on asteroids and planetary surfaces. By comparing the results of computer simulations with images of large craters on (21) Lutetia gathered as ESA's Rosetta spacecraft flew past the asteroid, scientists can reconstruct the details of the impacts that created them. In particular, these snapshots have been drawn from a simulation used to model the impact that created Massilia, the largest crater identified on Lutetia. With a diameter of 57 km, this crater provides evidence of the most dramatic event in the history of Lutetia.
As shown in the first snapshot, when a small cosmic body hits a large asteroid such as Lutetia, first a bowl-shaped cavity is produced on the asteroid's surface, while cracks start developing in the interior up to the surface due to propagation and reflection of stress waves from the impact. At the same time, streams of strongly shocked material – including a mixture of debris from both the 'projectile' and the target – arise from the crater, as indicated by the wing-shaped features visible in the first three snapshots. This debris will eventually fall back onto the asteroid's surface and coat the regions near the crater. In about an hour, the crater has already evolved into its final configuration, as shown in the fourth snapshot. This consists of a wider structure that formed via the collapse of the cavity's relatively steep rim onto the floor. While this process results in the production of a damaged layer close to the surface, the interior of the asteroid does not bear signs of substantial damage, except for some fractures close to the impact site and at its antipodes.
In the simulations, Lutetia has been modelled as a sphere with radius of 50 km, which is a reasonable approximation for these kind of studies. Comparing the results of the simulations with images of Massilia suggests that the 'projectile' responsible for producing this very wide crater was quite large, with a diameter of about 7.5 km. However, the probability of such a large body colliding with the asteroid is quite low, and so this must have occurred when Lutetia was relatively young. This dates the impact that led to the formation of Massilia to not long after the so-called Late Heavy Bombardment, a period in the early history of the Solar System when the flux of bodies impacting asteroids, planets and their satellites was significantly larger than it is at present.