A new approach to modelling impacts on rubble pile asteroid simulants

Abstract

Many asteroids with low bulk densities must have a rubble pile structure and internal voids. Although little is known about their internal structure, numerical simulations of impact events on these asteroids rely on assumptions on how the voids are distributed. We present a new approach to model impacts on rubble pile asteroids that explicitly takes into account their internal structure. The formation of the asteroid is modelled as a rubble pile aggregate of spherical pebbles of different sizes. This aggregate is then converted into a high-resolution smoothed particle hydrodynamics (SPH) model, accounting for macroporosity inside the pebbles. We compare impact-event outcomes for a large set of internal configurations to explore the parameter space of our model-building process. The analysis of the fragment size distribution and the disruption threshold quantifies the specific influence of each input parameter. The size distribution of the pebbles used in our model is a simple power law, containing three free parameters: the slope α, the lower cut-off radius r min and the upper cutoff radius r max . The influence of all three parameters on the outcome is assessed in this paper. The existence of void space in our model increases the resistance against collisional disruption, a behaviour previously reported based on numerical simulations using a continuum description of porous material (Holsapple 2009). We show, for a set of asteroid collisions typical for small asteroids in the main belt, that no a priori knowledge of the exact size distribution of the pebbles inside the asteroid is needed, as the choice of the corresponding parameters does not directly correlate with the impact outcome.

Far-Field Inversion for the Deep Interior Scanning CubeSat

“…The reconstruction of interior structures containing less contrast than the structure analyzed in this study might also prove more difficult, and the existence of multiple scattering surfaces in the interior might increase the signal to noise required for a good reconstruction. It is therefore planned to assess the reconstruction of more complex interior structures, as for example an interior filled with spherical monolithic fragments following a power law size distribution as motivated in [23], [24].…”

“…Rubble-pile asteroids are celestial bodies composed of aggregates bound together by gravitation and weak cohesion [18]- [24]. Therefore, they are likely to contain macroporosity, e.g., internal voids or cracks.…”

Rubble pile asteroids are forever

“…We attribute such a long duration to the shock-absorbent nature of rubble pile material during shock. Since rubble pile asteroids are extremely porous ( 27 ), pore collapses will absorb most of the increase of energy caused by the shock process rather than the energy being used to fracture solid rocks or to eject fragments away from Itokawa ( 30 , 31 ). Numerical simulations are in agreement with our results in that the energy threshold necessary to totally disrupt rubble pile asteroids is >4 times higher than for monolithic asteroids ( 30 ).…”

Multigrid-Based Inversion for Volumetric Radar Imaging With Asteroid Interior Reconstruction as a Potential Application

“…The present forward approach might, for example, be utilized in combination with an alternative inversion strategy. An important future direction regarding radio tomography would be to use a realistic 3D rubble pile asteroid model [44], [45], e.g., to optimize the number of resolution levels and the amount of compression.…”