Imaging polarimetry and photometry of comet 21P/Giacobini-Zinner

TL;DR

This study presents polarimetric observations of comet 21P/Giacobini-Zinner, revealing rapid particle replenishment in the coma and suggesting compositional variations influence polarization signals, with implications for comet activity.

Contribution

First detailed polarimetric analysis of comet 21P/Giacobini-Zinner highlighting particle replenishment timescales and compositional effects on polarization.

Findings

Particles in the coma are replenished within about one day.

Carbonaceous particles cause stronger positive polarization than silicates.

Polarization variations indicate jet-like activity and compositional differences.

Abstract

We report results of polarimetric observations of comet 21P/Giacobini-Zinner made at phase angles, {\alpha}=76-78 deg, between 10 and 17 of September 2018, and compare them with previous measurements. We find significant variations in the polarimetric signals that appear consistent with those reported previously. These variations and subsequent modeling suggest that the particles in the coma are replenished within a period of approximately one day. This period is significantly shorter for highly absorbing carbonaceous particles than for non-absorbing Mg-rich silicate particles. Such a difference in the relative abundances of these components can lead to variations in the polarization response of the coma. The strong positive polarization in the subsolar direction suggests a large relative abundance of carbonaceous material, which may be an indicator of jet-type activity.