Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition

TL;DR

This study provides detailed optical observations of NEA 162173 (1999 JU3) during 2011-2012, confirming key physical parameters such as rotational period and phase function to support the JAXA Hayabusa 2 mission.

Contribution

It offers new photometric data covering low phase angles and independently derives physical properties crucial for asteroid exploration missions.

Findings

Rotational period of 7.625 hours

Axis ratio a/b = 1.12

Absolute magnitude H_R = 18.69 mag

Abstract

Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid sample return missions, not only because of its accessibility but also because of the first C-type asteroid for exploration missions. The lightcurve-related physical properties of this object were investigated during the 2011-2012 apparition. We aim to confirm the physical parameters useful for JAXA's Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase function. Our data complement previous studies that did not cover low phase angles. With optical imagers and 1-2 m class telescopes, we acquired the photometric data at different phase angles. We independently derived the rotational lightcurve and the phase curve of the asteroid. We have analyzed the lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of 7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R = 18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained based on the observations made during the 2011-2012 apparition.