Imaging Polarimetry of Comet 67P/Churyumov-Gerasimenko: Homogeneous Distribution of Polarisation and its Implications

TL;DR

This study presents high-quality polarimetric measurements of Comet 67P from 2015 to 2021, revealing a homogeneous polarization distribution across the coma and tail, with implications for dust properties and observational techniques.

Contribution

It provides the first high signal-to-noise polarimetric phase curve of 67P, showing a homogeneous polarization distribution and analyzing the effects of image alignment on measurements.

Findings

Polarimetric phase curve resembles other Jupiter family comets.

Homogeneous polarization distribution in the coma and tail.

Marginal differences between pre- and post-perihelion data.

Abstract

Comet 67P/Churyumov-Gerasimenko (67P) become observable for the first time in 2021 since the Rosetta rendezvous in 2014--16. Here, we present pre-perihelion polarimetric measurements of 67P from 2021 performed with the Very Large Telescope (VLT), as well as post-perihelion polarimetric measurements from 2015--16 obtained with the VLT and the William Herschel Telescope (WHT). This new data covers a phase angle range of ~4-50{\deg} and presents polarimetric measurements of unprecedentedly high S/N ratio. Complementing previous measurements, the polarimetric phase curve of 67P resembles that of other Jupiter family comets and high-polarisation, dusty comets. Comparing pre- and post-perihelion data sets, we find only a marginal difference between the polarimetric phase curves. In our imaging maps, we detect various linear structures produced by the dust in the inner coma of the comet. Despite this, we find a homogeneous spread of polarisation around the photocentre throughout the coma and tail, in contrast to previous studies. Finally, we explore the consequences of image misalignments on both polarimetric maps and aperture polarimetric measurements.