The Formation of Asteroid Satellites in Catastrophic Impacts: Results from Numerical Simulations Daniel D. Durda, William F. Bottke, and Brian L. Enke (Southwest Research Institute) Erik Asphaug (University of California Santa Cruz) Derek C. Richardson and Zoe M. Leinhardt (University of Maryland)

The “Next Generation” of Numerical Models We are substantially improving upon past models by conducting detailed 3-dimensional smooth-particle hydrodynamics (SPH) models of collisions between asteroids, and then following the subsequent dynamics of ejected debris through fast, state-of-the-art N-body simulations. Benefits of this scheme: Rigorous treatment of impact physics, so that accurate fragment size distributions and velocity fields are established Far faster treatment of N-body dynamics with efficient mutual capture and collision detection capability

SPH Modeling 3D SPH code (Benz and Asphaug 1995) Material strength only, no gravity (the shock propagation and fragmentation time scales are less than the gravitational time scale) 100,000 particles in target; number of particles in impactor chosen to match particle volume density in target (resolution of ~2 km)

N-body Modeling Parallel tree code PKDGRAV (Leinhardt, Richardson, and Quinn 2000) Fast! Rapid detection and accurate treatment of low-speed collisions between fragments Supports arbitrary particle size distributions

Initial Conditions Target Information: 100 km in diameter Basalt ρ = 2.7 g cm-3

Initial Conditions We have completed 160 simulations over a range of parameters: V = 2.5-7 km s-1 θ = 15-75 Dimp = 10-46 km We track the ejecta for 4 days of simulation time

Types of Asteroid Satellites

Types of Asteroid Satellites

Types of Asteroid Satellites

Types of Asteroid Satellites

Key to Results

Key to Results

SMATS Results

SMATS Results

SMATS Results

EEB Results

EEB Results

EEB Results

EEB Results

EEB Results

EEB Results

Summary of Results to Date… We are able to produce a large number of satellite systems consistent with the systems observed to date through catastrophic and sub-catastrophic impacts. The large primaries of SMATS systems (like 762 Pulkova) are likely gravitationally reaccumulated rubble piles resulting from catastrophic impacts. There are likely a lot of undiscovered Ida-Dactyl like systems. Big, slow impactors striking at 30 produce a large number of EEBs (small, loosely-bound systems like 3749 Balam). A lot more of these types of systems remain to be found among the small main-belt asteroid population.

The modeling continues…