Positive YORP effect induced by lateral heat conduction in a crater

TL;DR

This study demonstrates that lateral heat conduction in craters on asteroids induces a positive YORP torque, significantly influencing their spin evolution, especially for small craters, with implications for observed asteroid spin states.

Contribution

It reveals that lateral heat conduction within craters causes a persistent positive YORP torque, a factor previously underexplored in asteroid spin dynamics.

Findings

Crater-induced YORP torque is consistently positive.

Lateral heat conduction is the primary cause of this torque in 3D models.

For small craters, the torque can be 10-100% of the normal YORP effect.

Abstract

The YORP effect plays an important role in the spin evolution of asteroids. Although craters are ubiquitous surface features, their influence on YORP torque has received limited attention. In this paper, we investigate the YORP torque of a circular crater on a spherical asteroid, focusing specifically on how lateral thermal conduction breaks symmetry to produce a net torque. Using three-dimensional finite element simulations, we calculate the resulting spin and obliquity accelerations and examine their dependence on the crater's location, depth, and thermal parameters. Our results show that the crater-induced spin torque is consistently positive, and craters at different latitudes drive the spin axis toward obliquity equilibria at 0, 90 or 180 degree. We demonstrate that the spin torque arises primarily from the lateral heat conduction inside the asteroid that occurs only in 3D model, while the contributions from self-heating and shadowing effects are negligible. While the YORP effect induced by internal heat conduction may be overtaken by torque components arising from shadowing and crater orientation, particularly on large asteroids, our numerical results show that for small craters, this spin torque amounts to approximately 10 to 100 percent of the normal YORP torque. Its persistent positivity may help explain the observed prevalence of positive spin accelerations in asteroids.