Daniel D. Durda, William F. Bottke, and Brian L. EnkeDaniel D. Durda, William F. Bottke, and Brian L. Enke(Southwest Research Institute)(Southwest Research Institute)

Erik AsphaugErik Asphaug(University of California Santa Cruz)(University of California Santa Cruz)

Derek C. Richardson and Zoe M. LeinhardtDerek C. Richardson and Zoe M. Leinhardt(University of Maryland)(University of Maryland)

The Formation of Asteroid Satellites in Catastrophic Impacts: Results from

Numerical Simulations

The “Next Generation” of Numerical Models

We are substantially improving upon past models by conducting We are substantially improving upon past models by conducting detailed 3-dimensional smooth-particle hydrodynamics (SPH) models detailed 3-dimensional smooth-particle hydrodynamics (SPH) models of collisions between asteroids, and then following the subsequent of collisions between asteroids, and then following the subsequent dynamics of ejected debris through fast, state-of-the-art dynamics of ejected debris through fast, state-of-the-art NN-body -body simulations. simulations.

Benefits of this scheme:Benefits of this scheme: Rigorous treatment of impact physics, so that accurate fragment size Rigorous treatment of impact physics, so that accurate fragment size

distributions and velocity fields are establisheddistributions and velocity fields are established

Far faster treatment of Far faster treatment of NN-body dynamics with efficient mutual capture and -body dynamics with efficient mutual capture and collision detection capabilitycollision detection capability

SPH Modeling

3D SPH code (Benz 3D SPH code (Benz and Asphaug 1995)and Asphaug 1995)

Material strength only, Material strength only, no gravityno gravity (the shock (the shock propagation and fragmentation propagation and fragmentation time scales are less than the time scales are less than the gravitational time scale)gravitational time scale)

100,000 particles in 100,000 particles in target; number of target; number of particles in impactor particles in impactor chosen to match chosen to match particle volume particle volume density in target density in target (resolution of ~2 km)(resolution of ~2 km)

N-body Modeling

Parallel tree code Parallel tree code PKDGRAVPKDGRAV (Leinhardt, (Leinhardt, Richardson, and Richardson, and Quinn 2000)Quinn 2000)

Fast!Fast! Rapid detection and Rapid detection and

accurate treatment of accurate treatment of low-speed collisions low-speed collisions between fragmentsbetween fragments

Supports arbitrary Supports arbitrary particle size particle size distributionsdistributions

Initial Conditions

100 km in diameter100 km in diameter BasaltBasalt ρρ = 2.7 g cm = 2.7 g cm-3-3

Target Information:Target Information:

Initial Conditions

We have completed We have completed 160 simulations over a 160 simulations over a range of parameters:range of parameters: VV = 2.5-7 km s = 2.5-7 km s-1-1

θθ = 15-75 = 15-75 DDimpimp = 10-46 km = 10-46 km

We track the ejecta for We track the ejecta for 4 days of simulation 4 days of simulation timetime

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 We are able to produce a large number of satellite systems consistent with the systems observed to date systems consistent with the systems observed to date through catastrophic and sub-catastrophic impacts.through catastrophic and sub-catastrophic impacts.

The large primaries of SMATS systems (like 762 The large primaries of SMATS systems (like 762 Pulkova) are likely gravitationally reaccumulated rubble Pulkova) are likely gravitationally reaccumulated rubble piles resulting from catastrophic impacts. There are piles resulting from catastrophic impacts. There are likely a lot of undiscovered Ida-Dactyl like systems.likely a lot of undiscovered Ida-Dactyl like systems.

Big, slow impactors striking at 30Big, slow impactors striking at 30 produce a large produce a large number of EEBs (small, loosely-bound systems like number of EEBs (small, loosely-bound systems like 3749 Balam). A lot more of these types of systems 3749 Balam). A lot more of these types of systems remain to be found among the small main-belt asteroid remain to be found among the small main-belt asteroid population.population.

The modeling continues…