Angular Momemtum of Binary Asteroids: Implication for their possible origin

TL;DR

This study analyzes the physical and orbital properties of binary asteroids, revealing that their angular momentum values suggest origins in rotational fission or mass shedding, and that angular momentum can indicate internal structure.

Contribution

It provides a detailed analysis of binary asteroid angular momentum, linking it to their possible formation mechanisms and internal structure, based on extensive observational data.

Findings

Separated binaries have total angular momentum close to the Maclaurin-Jacobi bifurcation value.

Contact binaries and tidally locked systems have higher angular momentum, matching fission equilibrium models.

Total angular momentum serves as a proxy for internal structure assessment.

Abstract

We describe in this work a thorough study of the physical and orbital characteristics of extensively observed main-belt and Trojan binaries, mainly taken from the LAOSA (Large Adaptive Optics Survey of Asteroids, Marchis et al., 2006c) database, along with a selection of bifurcated objects. Dimensionless quantities, such as the specific angular momentum and the primary spin rate, are computed and discussed for each system. They suggest that these asteroidal systems might be the outcome of rotational fission or mass shedding of a parent body presumably subjected to an external torque. One of the most striking features of separated binaries composed of a large primary (Rp > 100 km) with a much smaller secondary (Rs < 20 km) is that they all have total angular momentum of 0.27. This value is quite close to the Maclaurin-Jacobi bifurcation (0.308) of a spinning fluid body. Alternatively, contact binaries and tidally locked double asteroids, made of components of similar size, have an angular momentum larger than 0.48. They compare successfully with the fission equilibrium sequence of a rotating fluid mass. In conclusion, we find that total angular momentum is a useful proxy to assess internal structure of such systems.