Detection of Rotational Acceleration of Bennu using HST Lightcurve Observations

TL;DR

This study uses historical and Hubble Space Telescope observations to detect a small but significant acceleration in Bennu's rotation rate, contributing to understanding asteroid spin dynamics and the YORP effect.

Contribution

First detection of Bennu's rotational acceleration using multi-epoch observations, providing insights into asteroid spin evolution and the influence of YORP effect.

Findings

Detected a rotational acceleration of approximately 2.64 x 10^-6 deg/day^2

Observed rotation rate change consistent with YORP effect predictions

Future OSIRIS-REx data will clarify the cause of the acceleration

Abstract

We observed the near-Earth asteroid (101955) Bennu from the ground in 1999 and 2005, and with the Hubble Space Telescope in 2012, to constrain its rotation rate. The data reveal an acceleration of $2.64 \pm 1.05 \times 10^{-6} \mathrm{deg\ day}^{-2}$, which could be due to a change in the moment of inertia of Bennu or to spin up from the YORP effect or other source of angular momentum. The best solution is within 1 sigma of the period determined by Nolan et al. (2013). The OSIRIS-REx mission will determine the rotation state independently in 2019. Those measurements should show whether the change in rotation rate is a steady increase (due, for example, to the YORP effect) or some other phenomenon. The precise shape and surface properties measured by the OSIRIS-REx science team will allow for a better understanding of variations in rotation rate of small asteroids.