Positive YORP effect induced by lateral heat conduction in a crater

The Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect plays an important role in the spin evolution of asteroids. Although craters are ubiquitous surface features, their influence on the YORP torque has received limited attention. In this study, 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 3D finite element simulations, we calculated the resulting spin and obliquity accelerations and examined 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 towards obliquity equilibria at 0^̧irc, 90^̧irc, or 180^̧irc. We demonstrate that the spin torque arises primarily from the lateral heat conduction inside the asteroid that occurs only in 3D models, 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% -- 100% of the normal YORP torque. Its persistent positivity may help explain the observed prevalence of positive spin accelerations in asteroids.