Scott J. Kenyon, Benjamin C. Bromley
Motivated by the New Horizons mission, we consider how Pluto's small satellites -- currently P5, Nix, P4, and Hydra -- grow in debris from the giant impact that forms the Pluto-Charon binary or in solid material captured from the protoplanetary debris disk. If the satellites have masses close to their minimum masses, our analysis suggests that capture of material into a circumplanetary or circumbinary debris disk is a viable mechanism for satellite formation. If the satellites are more massive, they probably form in debris from the giant impact. After the impact, Pluto and Charon accrete some of the debris and eject the rest from the binary orbit. During the ejection, high velocity collisions among debris particles produce a collisional cascade, leading to the ejection of some debris from the system and enabling the remaining debris particles to find stable orbits around the binary. Our numerical simulations of viscous diffusion, coagulation, and migration show that collisional evolution within a ring or disk of debris leads to a few small satellites orbiting Pluto-Charon. These simulations are the first to demonstrate migration-induced mergers within a particle disk. The final satellite masses correlate with the initial disk mass. More massive disks tend to produce fewer satellites. For the current properties of the satellites, our results strongly favor initial debris masses of 3-10 times 10^{19} g and current satellite albedos A = 0.4--1. We also predict an ensemble of smaller satellites with radii of 1-3 km or less and very small particles with radii of 1-100 cm and optical depth tau <= 10^{-10}. These objects should have semimajor axes outside the current orbit of Hydra.
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http://arxiv.org/abs/1303.0280
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