Shape and spin axis determination of the Tianwen-2 target asteroid (469219) Kamo'oalewa from lightcurve inversion

TL;DR

This study models the shape and spin axis of asteroid Kamo'oalewa using lightcurve inversion, providing crucial data for the upcoming Tianwen-2 mission.

Contribution

First convex shape and spin axis model of Kamo'oalewa derived from photometric observations, aiding mission planning.

Findings

Determined the asteroid's spin pole at (126°, -16°) ecliptic coordinates.

Estimated the rotation period to be approximately 0.465 hours.

Provided the first direct constraints on the asteroid's shape and rotational state.

Abstract

Near-Earth asteroid (469219) Kamo'oalewa is an Earth quasi-satellite, temporarily trapped in a 1:1 orbital resonance with our planet. Despite its dynamical relevance and the hypothesis that it may be a lunar ejecta fragment, its physical properties are still poorly constrained. In particular, no reliable models of its shape and spin state have been published so far. The scientific interest in this object is further enhanced by its selection as the primary target of the Chinese Tianwen-2 mission, which aims to rendezvous with this asteroid and return samples of it to Earth. The aim of this work is to determine the shape and spin axis orientation of Kamo'oalewa by means of photometric telescope observations and lightcurve inversion. We analyzed lightcurves obtained during several apparitions using the well-established algorithm, based on convex shape modeling. We derived a convex shape model and estimated the spin pole orientation. In the preferred solution, the pole is located at ecliptic coordinates {\lambda}, {\beta} = (126,-16) degrees, with a sidereal rotation period of P~0.465 h. Conclusions. Our results provide the first direct constraints on the rotational state and morphology of Kamo'oalewa, information of key importance in preparation for the upcoming Tianwen-2 sample-return mission.