Systematic structure and sinks in the YORP effect

TL;DR

This paper explores the structured patterns of the YORP effect on asteroids, revealing a potential equilibrium state influenced by shape and surface features, which could impact asteroid spin evolution models.

Contribution

It introduces the concept of a YORP equilibrium state driven by shape and thermal transport, supported by estimates indicating its potential prevalence among asteroids.

Findings

10-20% of asteroids may be in YORP equilibrium

YORP effects can lead to long-term constant spin states

The equilibrium influences asteroid spin evolution theories

Abstract

There is a correlation between the components of the YORP effect of most asteroids, which drives the obliquity and spin rate of the affected bodies in a consistent pattern. This allows for a clear and unambiguous picture for how the spin rates and poles of asteroids affected by YORP will evolve and simplifies the overall picture for how populations will migrate on average. The YORP effect can also lead to a previously unexplored equilibrium state for affected bodies. This equilibrium state is a function of the usual "normal YORP" effect (which arises due to the global shape asymmetry of the asteroid) and the "tangential YORP" (which arises due the transport of thermal energy through rocky surface features). Estimates from current shape models show that 10-20\% of asteroids have the proper condition to be captured in this equilibrium state, indicating that the occurrence of this state may be significant. The existence of this attractor for the asteroid population means that objects affected by YORP may leave their usual YORP cycles and maintain a constant spin rate over long time periods -- this has significant implications for our interpretation of asteroid spin rate evolution and related theories for their physical evolution.

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