The Geometric Albedo of (4179) Toutatis Estimated from KMTNet DEEP-South Observations

TL;DR

This study estimates the geometric albedo of asteroid (4179) Toutatis using optical observations from KMTNet, confirming its S-type classification and surface grain properties, and compares it with previous data for consistency.

Contribution

The paper provides a new estimate of Toutatis's geometric albedo using ground-based optical data and shape modeling, enhancing understanding of its surface properties.

Findings

Toutatis has a geometric albedo of approximately 0.185.

The albedo estimate aligns with polarimetric and infrared data.

Surface grains are likely smaller than those on some near-Sun asteroids.

Abstract

We derive the geometric albedo of a near-Earth asteroid, (4179) Toutatis, to investigate its surface physical conditions. The asteroid has been studied rigorously not only via ground-based photometric, spectrometric, polarimetric, and radar observations but also via \textit{in situ} observation by the Chinese Chang'e-2 space probe; however, its geometric albedo is not well understood. We conducted V-band photometric observations when the asteroid was at opposition in April 2018 using the three telescopes in the southern hemisphere that compose the Korea Microlensing Telescope Network (KMTNet). The observed time-variable cross section was corrected using the radar shape model. We find that Toutatis has a geometric albedo $p_\mathrm{V} = 0.185^{+0.045}_{-0.039} $, which is typical of S-type asteroids. We compare the geometric albedo with archival polarimetric data and further find that the polarimetric slope--albedo law provides a reliable estimate for the albedo of this S-type asteroid. The thermal infrared observation also produced similar results if the size of the asteroid is updated to match the results from Chang'e-2. We conjecture that the surface of Toutatis is covered with grains smaller than that of the near-Sun asteroids including (1566) Icarus and (3200) Phaethon.