Analysis of CN Coma Morphology Features of Comet 21P/Giacobini-Zinner

Abstract

We analyze jet features found in the coma of Comet 21P/Giacobini-Zinner (21P/GZ) during its 2018 perihelion passage using narrowband CN photometric imaging in order to determine the comet's rotational period, and constrain the CN gas outflow velocity and rotational state through the analysis of azimuthally enhanced morphological features. We find that 21P/GZ has a period of either 7.39 $\pm$ 0.01 or 10.66 $\pm$ 0.01 hours. We measure a lower limit to the outflow velocity for the Northern Jet of 730 $\pm$ 30 m s$^{-1}$ and for the Southern Jet of 740 $\pm$ 30 m s$^{-1}$. We analyze the morphologies of the jet features and determine that the Northern jet possesses a corkscrew pattern, and utilize that knowledge to determine a rotational pole position at a Right Ascension of ${169^{+28}_{-23}}^{\circ}$ and a Declination of ${73^{+5}_{-11}}^{\circ}$, with undetermined sense of rotation.