Obliquity dependence of the tangential YORP

TL;DR

This paper investigates how the tangential YORP effect influences asteroid spin rates at various obliquities, revealing it operates beyond zero obliquity and diminishes with increasing obliquity.

Contribution

It extends the understanding of tangential YORP to arbitrary obliquities using numerical simulations, which was previously limited to zero obliquity cases.

Findings

Tangential YORP operates at non-zero obliquities.

The effect decreases by a factor of 2 as obliquity increases.

Numerical simulations confirm the obliquity dependence.

Abstract

Context. Tangential YORP is a thermophysical effect that can alter the rotation rate of asteroids and is distinct from the "normal" YORP effect, but to date has only been studied for asteroids with zero obliquity. Aims. The tangential YORP force produced by spherical boulders on the surface of an asteroid with an arbitrary obliquity is studied. Methods. A finite element method is used to simulate heat conductivity inside a boulder, to find the recoil force experienced by it. Then an ellipsoidal asteroid uniformly covered by such boulders is considered and the torque is numerically integrated over its surface. Results. Tangential YORP is found to operate on non-zero obliquities and decreases by a factor of 2 for increasing obliquity.