CN Morphology Studies of Comet 103P/Hartley 2

TL;DR

This study uses CN imaging over several months to analyze the changing coma morphology of Comet 103P/Hartley 2, revealing insights into its rotation, active regions, and pole orientation.

Contribution

It provides the first detailed morphological analysis of Hartley 2's CN features, including rotation period changes and pole orientation, based on extensive observational data.

Findings

Rotation period increased from 16.7 hr to 18.7 hr during the apparition.

Morphology varied from face-on spirals to side-on corkscrews.

Pole orientation is near RA=257°, Dec=+67°, with two active mid-latitude regions.

Abstract

We report on narrowband CN imaging of Comet 103P/Hartley 2 obtained at Lowell Observatory on 39 nights from 2010 July until 2011 January. We observed two features, one generally to the north and the other generally to the south. The CN morphology varied during the apparition: no morphology was seen in July; in August and September the northern feature dominated and appeared as a mostly face-on spiral; in October, November, and December the northern and southern features were roughly equal in brightness and looked like more side-on corkscrews; in January the southern feature was dominant but the morphology was indistinct due to very low signal. The morphology changed smoothly during each night and similar morphology was seen from night to night. However, the morphology did not exactly repeat each rotation cycle, suggesting that there is a small non-principal axis rotation. Based on the repetition of the morphology, we find evidence that the fundamental rotation period was increasing: 16.7 hr from August 13-17, 17.2 hr from September 10-13, 18.2 hr from October 12-19, and 18.7 hr from October 31-November 7. We conducted Monte Carlo jet modeling to constrain the pole orientation and locations of the active regions based on the observed morphology. Our preliminary, self-consistent pole solution has an obliquity of 10 deg relative to the comet's orbital plane (i.e., it is centered near RA = 257 deg and Dec=+67 deg with an uncertainty around this position of about 15 deg) and has two mid-latitude sources, one in each hemisphere.