A Pluto-Charon Concerto: An Impact on Charon as the Origin of the Small Satellites

TL;DR

This paper proposes that the small satellites of Pluto and Charon originated from debris generated by a significant impact on Charon, with the debris disk's evolution and impact parameters analyzed through simulations and estimates.

Contribution

It introduces a novel impact-based formation scenario for Pluto's small satellites, emphasizing a later impact on Charon rather than formation from primordial debris.

Findings

Impactor radius estimated at 30-100 km

Impact events were common in early solar system history

Impact scenario avoids destabilizing resonances during binary expansion

Abstract

We consider a scenario where the small satellites of Pluto and Charon grew within a disk of debris from an impact between Charon and a trans-Neptunian Object (TNO). After Charon's orbital motion boosts the debris into a disk-like structure, rapid orbital damping of meter-size or smaller objects is essential to prevent the subsequent re-accretion or dynamical ejection by the binary. From analytical estimates and simulations of disk evolution, we estimate an impactor radius of 30-100 km; smaller (larger) radii apply to an oblique (direct) impact. Although collisions between large TNOs and Charon are unlikely today, they were relatively common within the first 0.1-1 Gyr of the solar system. Compared to models where the small satellites agglomerate in the debris left over by the giant impact that produced the Pluto-Charon binary planet, satellite formation from a later impact on Charon avoids the destabilizing resonances that sweep past the satellites during the early orbital expansion of the binary.