Multi-epoch spectro-photometric characterization of the minimoon 2024 PT${}_5$ in the visible and near-infrared

Abstract

2024 PT${}_5$ is a tiny ($D\le 10$ m) near-Earth asteroid (NEA) discovered in August 2024. 2024 PT${}_5$ was gravitationally bound to the Earth-Moon system from September to November 2024 and classified as a minimoon. Several quick response observations suggest the lunar ejecta origin of 2024 PT${}_5$, while rotation state and albedo, essential properties to investigate its origin, are not well constrained. We performed visible to near-infrared multicolor photometry of 2024 PT${}_5$ from data taken using the TriColor CMOS Camera and Spectrograph (TriCCS) on the Seimei 3.8 m telescope during 2025 January 4-10. The Seimei/TriCCS observations of 2024 PT${}_5$ cover phase angles from 14 deg to 27 deg, and were obtained in the $g$, $r$, $i$, and $z$ bands in the Pan-STARRS system. In addition, we analyzed $Y$, $J$, $H$, and $K$ photometry taken with the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) on the Keck I 10-m telescope taken on 2025 January 16-17. Our lightcurves show brightness variations over time periods of several tens of minutes. We infer that 2024 PT${}_5$ is in a tumbling state and has a lightcurve amplitude of about 0.3 mag. Visible and near-infrared color indices of 2024 PT${}_5$, $g-r=0.567\pm 0.044$, $r-i=0.155\pm 0.009$, $r-z=0.147\pm 0.066$, $Y-J=0.557\pm 0.046$, $J-H=0.672\pm 0.078$, and $H-Ks=0.148\pm 0.098$, indicate that 2024 PT${}_5$ is an S-complex asteroid, largely consistent with previous observations. Using the $H$-$G$ model, we derived an absolute magnitude $H_{V,HG}$ of $27.72\pm 0.09$ and a slope parameter $G_V$ of $0.223\pm 0.073$ in V-band. A geometric albedo of 2024 PT${}_5$ is derived to be $0.26\pm 0.07$ from the slope of its photometric phase curve. This albedo value is typical of the S- and Q-type NEAs. The color properties of 2024 PT${}_5$ derived from our observations match rock samples taken from the lunar surface, which agrees with previous studies.

Accepted for publication in Astronomy & Astrophysics (A&A). Abstract shortened for arXiv. Any comments are welcome

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