Constraining the Interiors of Asteroids Through Close Encounters

TL;DR

This paper introduces a method to infer asteroid interior density distributions by analyzing variations in angular velocity during close Earth encounters, using synthetic data and a new toolkit called AIME.

Contribution

The study develops a novel approach and a computational toolkit for constraining asteroid interiors from close encounter rotational data, including sensitivity and accuracy assessments.

Findings

High precision in rotational period (<~0.27s) is essential.

Low perigee distances (<~18 Earth radii) improve density resolution.

Large-scale density variations can be detected with ~0.1% uncertainty.

Abstract

Knowledge of the interior density distribution of an asteroid can reveal its composition and constrain its evolutionary history. However, most asteroid observational techniques are not sensitive to interior properties. We investigate the interior constraints accessible through monitoring variations in angular velocity during a close encounter. We derive the equations of motion for a rigid asteroid's orientation and angular velocity to arbitrary order and use them to generate synthetic angular velocity data for a representative asteroid on a close Earth encounter. We develop a toolkit AIME (Asteroid Interior Mapping from Encounters) which reconstructs asteroid density distribution from these data, and we perform injection-retrieval tests on these synthetic data to assess AIME's accuracy and precision. We also perform a sensitivity analysis to asteroid parameters (e.g., asteroid shape and orbital elements), observational set-up (e.g., measurement precision and cadence), and the mapping models used. We find that high precision in rotational period estimates (<~0.27 seconds) are necessary for each cadence, and that low perigees (<~18 Earth radii) are necessary to resolve large-scale density non-uniformities to uncertainties ~0.1% of the local density under some models.