The Influence of Rough Surface Thermal-Infrared Beaming on the Yarkovsky and YORP Effects

TL;DR

This paper adapts a thermophysical model to include surface roughness effects, revealing that rough surface thermal-infrared beaming significantly influences asteroid Yarkovsky and YORP effects, affecting their orbital and rotational evolution predictions.

Contribution

It introduces a new model accounting for surface roughness in predicting Yarkovsky and YORP effects, highlighting the importance of surface roughness details for accurate asteroid dynamics.

Findings

Rough surface thermal-infrared beaming enhances Yarkovsky drift by up to a factor of two.

YORP rotational acceleration is dampened by up to a third due to surface roughness.

Yarkovsky drift depends on average roughness, while YORP is sensitive to roughness distribution.

Abstract

It is now becoming widely accepted that photon recoil forces from the asymmetric reflection and thermal re-radiation of absorbed sunlight are, together with collisions and gravitational forces, primary mechanisms governing the dynamical and physical evolution of asteroids. The Yarkovsky effect causes orbital semi-major axis drift and the YORP effect causes changes in the rotation rate and pole orientation. We present an adaptation of the Advanced Thermophysical Model (ATPM) to simultaneously predict the Yarkovsky and YORP effects in the presence of thermal-infrared beaming caused by surface roughness, which has been neglected or dismissed in all previous models. Tests on Gaussian random sphere shaped asteroids, and on the real shapes of asteroids (1620) Geographos and (6489) Golevka, show that rough surface thermal-infrared beaming enhances the Yarkovsky orbital drift by typically tens of percent but it can be as much as a factor of two. The YORP rotational acceleration is on average dampened by up to a third typically but can be as much as one half. We find that the Yarkovsky orbital drift is only sensitive to the average degree, and not to the spatial distribution, of roughness across an asteroid surface. However, the YORP rotational acceleration is sensitive to the surface roughness spatial distribution, and can add significant uncertainties to the predictions for asteroids with relatively weak YORP effects. To accurately predict either effect the degree and spatial distribution of roughness across an asteroid surface must be known.