Speaker
Description
The vast majority of asteroids that pose a threat to Earth have a complex distribution of porosity due to their rubble-pile configuration. As of right now the only proven method for deflecting these potentially hazardous bodies is to use a kinetic impactor, as was demonstrated by the Double Asteroid Redirection Test (DART) mission. Kinetic impacts change the momentum of the target asteroid through the transfer of momentum of the impactor to the body and through the resulting ejection of material away from the target body. There are multiple material properties that affect the ejection of material from kinetic impacts, one of which being porosity, which plays a significant role in the cratering process. The crushing of pore space is an irreversible process that dissipates shock waves and decreases the free energy of the system. Additionally, the type of porosity, such as large open voids between individual boulders (macroporosity) and small well distributed voids within the boulders themselves (microporosity), could play a significant role during the creation of ejecta.
We have begun systematically testing how porosity distributions affect the deflection of rubble-pile asteroids by kinetic impacts using simulations performed with the Smooth Particle Hydrodynamics (SPH) code Spheral++. Spheral++ has recently been updated to include a Soft-Sphere Discrete Element Method (SSDEM) physics package. For this project, we first assemble our rubble-pile asteroids in the SSDEM package and then hand off the configuration to SPH to model the hypervelocity kinetic impact. We initialize the rubble piles with varying amounts of macro- and microporosity and observe the changes in ejected material to determine how the asteroid’s momentum changes accordingly. For the initial foray into this project, all simulations are performed in 2D to reduce simulation time and determine overall trends in impact response. We find that the inclusion of resolved macroporosity greatly reduces ejecta generation compared to an otherwise identical simulation with a microporous monolithic target and therefore significantly influences the deflection of asteroids. Our preliminary results demonstrate that, when designing asteroid deflection missions, the effects of both macro- and microporosity should be considered to accurately model the response of rubble-pile asteroids to mitigation attempts.
LLNL-ABS-2001234
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.