Near-Earth Binaries and Triples: Origin and Evolution of Spin-Orbital Properties

TL;DR

This study investigates the origins and evolution of spin-orbital properties in near-Earth binary and triple asteroid systems, finding that a combination of post-fission dynamics and tidal evolution explains most observed characteristics.

Contribution

It demonstrates that post-fission dynamics combined with tidal evolution can account for the observed spin-orbital configurations of near-Earth binaries and triples, clarifying their evolutionary pathways.

Findings

Post-fission dynamics and tidal evolution explain most observed properties.

Other mechanisms like BYORP, planetary encounters, are not essential.

Evolutionary pathways include various spin-orbit state transitions.

Abstract

In the near-Earth asteroid population, binary and triple systems have been discovered with mutual orbits that have significant eccentricities as well as large semi-major axes. All known systems with eccentric orbits and all widely-separated primary-satellite pairs have rapidly rotating satellites. Here we study processes that can elucidate the origin of these spin-orbital properties. Binary formation models based on rotational fissioning can reproduce asynchronous satellites on orbits with high eccentricities and a wide range of separations, but do not match observed properties. We explore whether any evolutionary mechanisms can link the spin and orbital parameters expected from post-fission dynamics to those observed today. We investigate four processes: tidal torques, radiative perturbations (BYORP), close planetary encounters, and Kozai oscillations. We find that a combination of post-fission dynamics and tidal evolution can explain nearly all the spin-orbit properties in a sample of nine well-characterized near-Earth binaries and triples. The other mechanisms may act but are not required to explain the observed data. Lastly, we describe evolutionary pathways between observed spin-orbital states including synchronous and circular, asynchronous and circular, and asynchronous and eccentric configurations.