Effect of Density Inhomogeneity on YORP: The case of Itokawa

TL;DR

This paper investigates how density inhomogeneities within asteroids like Itokawa influence the YORP effect, showing that mass distribution shifts can significantly alter predicted rotational changes and offering a method to infer internal density variations.

Contribution

It introduces a correction method for YORP predictions accounting for density inhomogeneity and demonstrates its application to Itokawa, linking YORP sensitivity to internal mass distribution.

Findings

YORP rate is sensitive to center of mass offsets

A 10-meter shift can reverse the YORP effect sign

Density distribution influences YORP detectability

Abstract

The effect of density inhomogeneity on the YORP effect for a given shape model is investigated. A density inhomogeneity will cause an offset between the center of figure and the center of mass and a re-orientation of the principal axes away from those associated with the shape alone. Both of these effects can alter the predicted YORP rate of change in angular velocity and obliquity. We apply these corrections to the Itokawa shape model and find that its YORP angular velocity rate is sensitive to offsets between its center of mass and center of figure, with a shift on the order of 10 meters being able to change the sign of the YORP effect for that asteroid. Given the non-detection of YORP for Itokawa as of 2008, this can shed light on the density distribution within that body. The theory supports a shift of the asteroid center of mass towards Itokawa's neck region, where there is an accumulation of finer gravels. Detection of the YORP effect for Itokawa should provide some strong constraints on its density distribution. This theory could also be applied to asteroids visited by future spacecraft to constrain density inhomogeneities.