Umov effect in asteroid (3200) Phaethon

Abstract

Context. The near-Earth asteroid (3200) Phaethon occasionally reveals a comet-like activity. It is a parent body to the Geminid meteor shower and considered as a target for the space mission called Demonstration and Experiment of Space Technology for Interplanetary Voyage Phaethon Flyby Dust Science, DESTINY + . Aims. We aim to characterize Phaethon through measurements of the degree of linear polarization P measured on Phaethon at large phase angles on its closest approach to Earth on December 17, 2017. These observations allow a more accurate estimation of the maximum value of the degree of linear polarization P max of Phaethon, and therefore, of studying the Umov effect. Methods. We performed polarimetric measurements of Phaethon at large phase angles α and thus constrained its P max . We also estimated the geometric albedo a based on the data available in the literature. The obtained P max and A were analysed with the Umov effect previously derived for the Moon that establishes an inverse linear correlation between log(P max ) and log(A) in the lunar regolith. Results. Our polarimetric observations of Phaethon in the visible reveal the degree of linear polarization P ≈ (17.23 ± 2.00)% at α ≈ 57.9 • and P ≈ (31.86 ± 2.00)% at α ≈ 73.2 • , which demonstrates no significant wavelength dependence within the error bars of our measurements (±2%). These data, when combined with what has previously been reported in the literature, suggests at least three types of polarimetric response on Phaethon. For two of them, we infer the maximum linear polarization to be P max ≈ 57.9%, occurring at α max = 131 • and P max ≈ 44.5% occurring at α max = 127 • . We estimate the geometric albedo (adjusted to α = 3 • ) to be A R = 0.075 ± 0.007 in the R filter, which appears to be consistent with dark F-type asteroids, as which Phaethon was first classified. We examine the Umov diagrams previously inferred for lunar regolith and find that they are hardly applicable to Phaethon and therefore not to other asteroids either.

Low-albedo asteroids: analogues with a high polarization at large phase angles

“…(iii) Phaethon data correspond to 5 sets obtained in red and visible domains, at different epochs (lower curve data from observations on 27 November to 24 January 2022 (Devogèle et al 2018;Shinnaka et al 2018;Kiselev et al, 2022;Geem al., 2022). Above and with a common region up to 30° with the previous curve, data from observations in the red domain obtained in September-October 2016 can be noticed (Ito et al, 2018), as well as two data points obtained in December 16-17 2017 without any filter, which are noted '2017z' (Zheltobryukhov et al 2018). The PPC for 2005 UD is close to the polarization obtained for Phaethon in 1996 (Devogèle et al 2020;Ishiguro et al 2021).…”

Asteroid (3200) Phaethon: results of polarimetric, photometric, and spectral observations

“…2010) and, therefore, its surface may change over time. IR photometry (radiometric diameter D = 4.7 ± 0.5 km), (Green et al 1985) 0.098 0.11 ± 0.01 IRAS albedo (Tedesco et al 1992) IRAS database, STM model (Tedesco et al 1992) 0.1066 ± 0.011 IRAS observations, D = 5.10 ± 0.2 km (Tedesco et al 2002(Tedesco et al , 2004 (Kareta et al 2018) Combination of radar diameter and photometry data (Ito et al 2018) 0.14 ± 0.04 (0.065  0.002) Polarimetry, slope-albedo relation (Shinnaka et al 2018) (the value revised in this work) 0.075 ± 0.007 (pv) Polarimetry (Zheltobryukhov et al 2018…”

“…Shinnaka et al (2018) also obtained the phase-polarization curve for Phaethon for a wide range of α from 19° to 114° with Pmax not less than 42.4% at max not less than 114.3°. In the 2017 apparition, polarization of Phaethon was also measured by Zheltobryukhov et al (2018) at phase angles 57. 9 and 73.2 and Okazaki et al (2020) at phase angles 33.4 and 57.9.…”

Photometric observations of the asteroid 3200 Phaethon using small and middle telescopes

“…It is in contrast with typical cometary nuclei that are slightly reddish in general (Tedesco & Desert, 2002). Zheltobryukhov et al (2018) estimated the geometric albedo of Phaethon to be 0.075 ± 0.007 in the R filter, which appears to be consistent with dark F-type asteroids. Also our data confirmed the taxonomy F-type of Phaethon.…”