Fragment properties at the catastrophic disruption threshold: The effect of the parent body’s internal structure

Abstract

Numerical simulations of asteroid break-ups, including both the fragmentation of the parent body and the gravitational interactions between the fragments, have allowed us to reproduce successfully the main properties of asteroid families formed in different regimes of impact energy, starting from a non-porous parent body. In this paper, using the same approach, 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. Thanks to our recent implementation of a model of fragmentation of porous materials, we can characterize Q * D for both porous and non-porous targets with a wide range of diameters. We can then analyze 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 the main outcome properties used by collisional models to study the evolutions of the different populations of small bodies. We also check the dependency of Q * D on the impact speed of the projectile. In the strength regime, which corresponds to target sizes below a few hundreds of meters, we find that porous targets are more difficult to disrupt than non-porous ones. In the gravity regime, the outcome is controlled purely by gravity and porosity in the case of porous targets. In the case of non-porous targets, the outcome also depends on strength. Indeed, decreasing the strength of non-porous targets make them easier to disrupt in this regime, while increasing the strength of porous targets has much less influence on the value of Q * D . Therefore, one cannot say that non-porous targets are systematically easier or more difficult to disrupt than porous ones, as the outcome highly depends on the assumed strength values. In the gravity regime, we also confirm that the process of gravitational reaccumulation is at the origin of the largest remnant's mass in both cases. We then propose some power-law relationships between Q * D and both target's size and impact speed that can be used in collisional evolution models. The resulting fragment size distributions can also be reasonably fitted by a power-law whose exponent ranges between −2.2 and −2.7 for all target diameters in both cases and independently on the impact velocity (at least in the small range investigated between 3 and 5 km/s). Then, although ejection velocities in the gravity regime tend to be higher from porous targets, they remain on the same order as the ones from non-porous targets.3

How primordial is the structure of comet 67P?

“…This result reflects the dissipative properties of material porosity and is consistent with previous studies (e.g. Jutzi et al 2010).…”

A new approach to modelling impacts on rubble pile asteroid simulants

“…8). This effect is explained by the energy needed to compress the voids and has been observed before (Holsapple 2009), and the values for Q * S found are in agreement with scaling laws derived by Jutzi et al (2010a), while the generalized scaling law for the gravitational disruption regime by Leinhardt & Stewart (2011) can not be applied. The next step, using our rubble pile models to test how changes in the interior configuration due to impacts can influence surface features, will be the subject of a future paper.…”

“…This linear relationship is characterized by a constant offset c * to the specific gravitational binding energy. The authors find a value of c * = 5 ± 2 to be representative for small bodies in the gravitational regime, which they define as bodies larger than 300 m. In the simulations discussed in our paper, e. g. v imp = 5.5 km s A study by Jutzi et al (2010a) focusses on the transition from strength to gravity regime for solid bodies as well as bodies con- Figure 9. Relative mass of the largest remnant as a function of the void fraction in the gravitational aggregate for all simulation configurations described in Table 3, experiment 1.…”

“…Many approaches use a homogeneous material assuming a distribution of sub-resolution voids, and equation of state and material model implement a local filling factor (e.g. Jutzi et al 2010a). So far, the following approaches have been tried to explicitly model the internal structure of rubble pile asteroids: Benavidez et al (2012) introduced a rubble pile model where the asteroid is represented as a spherical shell filled with an uneven distribution of basalt spheres, with radii ranging from 8 to 20 per cent of the radius of the parent body.…”

The Collisional Evolution of Undifferentiated Asteroids and the Formation of Chondritic Meteoroids

“…A catastrophic collision of a target body occurs when it collides with an impactor that carries sufficient energy to cause the largest remnant to possess 50% of the initial target mass. Jutzi et al (2010) calculated that a catastrophic collision occurs when a projectile with ∼ 27 km radius hits a porous target with 100 km radius. For target radii of 10 km, an object of ∼ 1 km radius is sufficient to catastrophically disrupt the target.…”