Catastrophic Impact Energy Threshold for Disruption of Small Porous and Non-Porous Asteroids: a Crucial Information for Deflection Strategies
Michel, Patrick¹; Jutzi, M.²; Benz, W.²; Richardson, D.C.^3
1University of Nice-Sophia Antipolis, Côte d'Azur Observatory; ²University of Bern; ³University of Maryland

Numerical simulations of asteroid break-ups, including both the fragmentation of the parent body and the gravitational interactions of the fragments, have allowed us to reproduce successfully the main properties of asteroid families formed in different regimes of impact energy from a non-porous parent body. Here, using the same kind of simulations, we concentrate on a single regime of impact energy, the so-called catastrophic threshold usually designated by Q*D, which results in the escape of half of the target's mass. This threshold can be used as a limit for deflecting an object instead of disrupting it. Thanks to our recent implementation of a model of fragmentation of porous materials in our hydrocode, we can characterize Q*D for both porous and non-porous targets, considering a wide range of diameters. We can then analyse the potential influence of porosity on the value of Q*D and by computing the gravitational phase of the collision in the gravity regime, we can characterize the collisional outcome in terms of the fragment size and ejection speed distributions, which are also useful information for the design of deflection space mission.

We will present our results in both the strength regime, which corresponds to target sizes below a few hundreds of meters, and the gravity one at larger sizes. We will show the effect of porosity on the value of Q*D and on the impact outcome. We will then concentrate on bodies in the range of sizes of Apophis (about 300 meters) to perform a more detailed analysis of the dependency of Q*D on the impact velocity, so that our results can be useful in the context of a high-velocity impact by a projectile for deflection purposes.

Obviously, the parameter space is huge. In particular, we only considered a limited set of material properties to characterize our porous and non-porous targets, and we plan to continue our investigations using a wider range of material properties to check whether our results can be generalized or need to be extended. This will help answering a question often ask about the assessment of the risk of disrupting a threatening object instead of deflecting it.