Surface structure and assessment of dust productivity of the cometary nucleus C/2017 K2 (PANSTARRS)

Abstract

C/2017 K2 (PANSTARRS) is a dynamically new hyperbolic comet that has exhibited activity at an extremely large heliocentric distance of 23.75 au. Observations of comet C/2017 K2 were performed at Mayaki observational station of the Astronomical Observatory of Odesa I. I. Mechnikov National University using the OMT--800 telescope with a FLI MicroLine 9000 camera during March--September 2021. Throughout the period of observations, the heliocentric distance of the comet has decreased from 6.8 to 5.4 au amid irregular fluctuations in the absolute magnitude within 5.0-6.2m. In the meantime, the value Af{\rho} has varied in the range of 6500-9800 cm. Such high values of the parameters are indicative of significant activity of the comet. Variations in the comet`s brightness hardly affect the shape of isophotes, which are nearly spherical in shape. It is only from April onwards that one can observe a slight elongation in the direction opposite to that in which the comet is heading, due to the dust tail being seen as projected onto the coma. Applying simple rotational gradient filter (simple subtraction) to composite images of the comet enabled us to detect the cometary nucleus spinning westward as measured from the North in the plane of projection. The widths of spiral structures in the coma that appear due to the nucleus spinning suggests the presence of a large-scale inhomogeneity in the distribution of volatiles on the nucleus surface. From July onwards, a new feature can be observed in the images processed using digital filters. Its position and shape have barely changed, which suggests that the area of activity responsible for the formation of this feature is likely located near the northern rotational pole of the cometary nucleus.