The phase-polarization curve of asteroid (3200) Phaethon

TL;DR

This study presents a detailed multi-colour phase-polarization curve of asteroid (3200) Phaethon, revealing high polarization values and supporting its classification as an asteroid similar to Pallas, though further data is needed for confirmation.

Contribution

The paper provides the first comprehensive phase-polarization curve of Phaethon in the positive polarization branch, offering new insights into its physical nature and polarization characteristics.

Findings

Measured high linear polarization values, among the highest for Solar system bodies.

Indications that the polarization maximum occurs around 130° phase angle with over 45% polarization.

Results support the asteroid hypothesis for Phaethon, similar to asteroid (2) Pallas.

Abstract

A multi-colour phase-polarization curve of asteroid (3200)~Phaethon has been obtained during the December 2017 apparition by merging measurements taken at the observing station of Calern (France) and at the Rhozen observatory (Bulgaria). All the observations were obtained in the positive polarization branch, the phase angle ranging from 36$^\circ$ to 116$^\circ$. The measured values of linear polarization are among the highest ever observed for a Solar system body. The covered interval of phase angle was not sufficiently extended to derive a firm determination of the $P_{\rm max}$ parameter, but this appears to occur at a phase angle around 130$^\circ$ and reaches more than 45\% of linear polarization. Phaethon is the parent body of the Geminid meteor shower, and the real physical nature of this object (asteroid or comet) has been a long-debated subject. Our polarimetric measurements seem to support the asteroid hypothesis with a phase-polarization curve similar to the asteroid (2)~Pallas, but further observations at smaller phase angles are needed to draw definitive conclusions.