Dynamical Constraints on the Origin of Main Belt Comets

TL;DR

This study uses numerical simulations to investigate the origin of Main Belt Comets, providing evidence that they formed in-place from asteroid family collisions, particularly the Themis family, rather than being captured comets from the outer solar system.

Contribution

It offers the first detailed dynamical analysis supporting in-situ formation of MBCs from asteroid family breakups, especially the Themis family, and rules out a cometary origin.

Findings

MBCs likely formed in-place from asteroid collisions.

Themis family identified as the probable source of MBCs.

Many stable orbits near the Themis family suggest more undiscovered MBCs.

Abstract

In an effort to understand the origin of the Main Belt Comets (MBCs) 7968 Elst-Pizzaro, 118401, and P/2005 U1, the dynamics of these three icy asteroids and a large number of hypothetical MBCs were studied. Results of extensive numerical integrations of these objects suggest that these MBCs were formed in-place through the collisional break up of a larger precursor body. Simulations point specifically to the Themis family of asteroids as the origin of these objects and rule out the possibility of a cometary origin (i.e. inward scattering of comets from outer solar system and their primordial capture in the asteroid belt). Results also indicate that while 7968 Elst-Pizzaro and 118401 maintain their orbits for 1 Gyr, P/2005 U1 diffuses chaotically in eccentricity and becomes unstable in ~20 Myr. The latter suggest that this MBC used to be a member of the Themis family and is now escaping away. Numerical integrations of the orbits of hypothetical MBCs in the vicinity of the Themis family show a clustering of stable orbits (with eccentricities smaller than 0.2 and inclinations less than 25 deg.) suggesting that many more MBCs may exist in the vicinity of this family (although they might have not been activated yet). The details of the results of simulations and the constraints on the models of the formation and origins of MBCs are presented, and their implications for the detection of more of these objects are discussed.