Capture of Irregular Satellites via Binary Planetesimal Exchange Reactions in Migrating Planetary Systems

TL;DR

This paper investigates how migrating planets can capture irregular satellites through binary planetesimal exchange reactions, highlighting the importance of slow, close encounters especially with outer planets, and estimating capture probabilities relevant to exoplanetary systems.

Contribution

It introduces a numerical method to analyze encounter distributions and estimates the likelihood of irregular satellite capture during planetary migration, emphasizing the role of binary planetesimals.

Findings

Outer planets have more close, slow encounters with planetesimals.

Estimated 1/100 chance of capturing a binary's secondary as an irregular satellite.

Captured satellites could explain observed features around exoplanets like Fomalhaut b.

Abstract

By logging encounters between planetesimals and planets we compute the distribution of encounters in a numerically integrated two planet system that is migrating due to interactions with an exterior planetesimal belt. Capture of an irregular satellite in orbit about a planet through an exchange reaction with a binary planetesimal is only likely when the binary planetesimal undergoes a slow and close encounter with the planet. In our simulations we find that close and slow encounters between planetesimals and a planet primarily occur with the outermost and not innermost planet. Taking care to consider where a planet orbit crossing binary planetesimal would first be tidally disrupted, we estimate the probability of both tidal disruption and irregular satellite capture. We estimate that the probability that the secondary of a binary planetesimal is captured and becomes an irregular satellite about a Neptune mass outer planet is about 1/100 for binaries with masses and separations similar to transneptunian planetesimal binaries. If young exoplanetary debris disks host a binary planetesimal population then outwards migrating outer planets should host captured irregular satellite populations. We discuss interpretation of emission associated with the exoplanet Fomalhaut b in terms of collisional evolution of a captured irregular satellite population that is replenished due to planetary migration.