Formation of satellites around large asteroids

Known satellites orbiting asteroids larger than ~100 km are found preferentially around primary bodies with rotation periods 5-6 h. This is significantly more rapid rotation than is typical for asteroids this large, which have an average rotation period closer to 10 hours. Similarly, the primaries of the satellite systems are more elongated than average as measured by lightcurve amplitudes and direct imaging. Finally, there are no known satellites around large S-type asteroids.

Numerical simulation has found that satellite formation is possible in large collisions between asteroids. However, tracking the shape and spin of the remnant bodies is computationally expensive and has thus not been performed for wide parameter spaces. Therefore, the relationship between impacts that form satellites and remnant spin and shape hasn't been previously utilized for understanding the key physics at play.

We present impact models of asteroid collisions typical of the Main Asteroid Belt. A hydrodynamic model of the impact is performed and the outcome is handed off to N-body gravitational models. The N-body modeling is done with pkdgrav, which is capable of modeling granular mechanical interactions. This allows for the evolving shape of the various remnants to be tracked throughout the reaccumulation process. We simulate head-on and oblique impacts into spherical targets that have a range of pre-impact rotation rates.

A dynamical stability map for close-in and eccentric orbits is created for each of the simulation outcomes shape and spin. This is used to determine which impact ejecta is placed onto long-term stable orbits as direct outcomes of the impact circumstances. We find that a direct pathway to stable satellites exists for impact outcomes that produce rapidly rotating and elongated remnants. The rapid rotation and elongation can be the result of pre-impact rotation or highly oblique impacts.