Non-principal axis rotation in binary asteroid systems and how it weakens the BYORP effect

TL;DR

This paper investigates how non-principal axis rotation in binary asteroid secondaries affects tidal evolution and the BYORP effect, revealing that such rotation can be long-lived and significantly alter orbital migration.

Contribution

It introduces viscoelastic mass/spring simulations to study the impact of non-principal axis rotation on binary asteroid dynamics and BYORP torque modulation.

Findings

Non-principal axis rotation can be long-lived after spin synchronization.

Rotation can be resonantly excited during orbital migration.

Non-principal axis rotation reduces or reverses BYORP torque.

Abstract

Using viscoelastic mass/spring model simulations, we explore tidal evolution and migration of compact binary asteroid systems. We find that after the secondary is captured into a spin-synchronous state, non-principal axis rotation in the secondary can be long-lived. The secondary's long axis can remain approximately aligned along the vector connecting secondary to primary while the secondary rocks back and forth about its long axis. Inward orbital semi-major axis migration can also resonantly excite non-principal axis rotation. By estimating solar radiation forces on triangular surface meshes, we show that the magnitude of the BYORP effect induced torque is sensitive to the secondary's spin state. Non-principal axis rotation within the 1:1 spin-orbit resonance can reduce the BYORP torque or cause frequent reversals in its direction.