Brightness, Colour, Polarisation: A Multi-Instrument Observation Campaign of the Gorizont-6 Satellite

TL;DR

This study demonstrates that combined multi-colour photometry and polarimetry effectively determine the rotation state of the Gorizont-6 satellite, revealing a YORP-driven spin-down over nine months.

Contribution

It introduces a multi-instrument observational approach that enhances the accuracy of satellite spin characterization by integrating photometry and polarimetry.

Findings

Multi-colour photometry improves period measurement robustness.

Polarimetry provides decisive constraints on spin-axis orientation.

The satellite's rotation period increases steadily, consistent with YORP effects.

Abstract

We present a coordinated multi-instrument photometric and polarimetric study of the defunct geosynchronous satellite, Gorizont-6. This observation campaign combined wide-field multi-colour observations with simultaneous multi-site photometry and linear polarimetry. Our results demonstrate that the combined simultaneous colour and polarimetric measurements aid in breaking the degeneracy between the fundamental spin period and its harmonics, enabling light curve features to be associated with specific reflecting surfaces. Using phase-dispersion minimisation with bootstrap resampling, we then measure a steadily increasing rotation period across six epochs spanning nine months, well described by a damped exponential curve consistent with Yarkovsky O'Keefe Radzievskii Paddack (YORP) driven spin-down. A geometrical analysis of the multi-site observations provides additional constraints on the spin-axis orientation based on paired glint events. Overall, multi-colour photometry yields efficient, robust period measurements compared with single-band data, while polarimetry supplies the decisive constraints needed for unambiguous rotation-state determination, highlighting the value of combined photometric-polarimetric strategies for characterising defunct satellites.