Abstract Under favorable conditions, high-resolution long-slit infrared spectroscopic observations of comets can provide information on how ices are associated within the nucleus from spatially resolved properties of volatiles in the coma. In this study, we demonstrate the utility of this technique by investigating two Jupiter-family comets that were observed close to Earth—73P-Schwassmann–Wachmann (fragments B and C) and 103P/Hartley 2—providing high spatial resolution from ground-based observations. Spectra of these comets were acquired with NIRSPEC at the W. M. Keck Observatory. Molecular emissions were sufficiently strong to obtain spatial distributions of column densities and rotational temperatures for H 2 O, C 2 H 6 , HCN, and CH 3 OH (for 103P only). Comparison of 73P-B and 73P-C coma properties and nucleus associations test the heterogeneity of processes in comets that were originally part of a single nucleus. The spatial distributions of molecular column densities and rotational temperatures are notably similar in 73P-B and 73P-C despite different activity levels, providing additional and independent evidence of a remarkably homogeneous 73P parent nucleus. Comparison of coma properties and nucleus associations in 73P and 103P test the heterogeneities of processes between comets with very different chemical compositions. Both comets show strong evidence of abundant coma icy grains that contain less-abundant volatiles in addition to H 2 O. Because icy grains are constituents of the nucleus, the presence of volatiles within these grains provides evidence for how ices are associated within the nuclei of these comets. The spatial distributions of molecular column densities and rotational temperatures suggest different nucleus ice associations for 73P and 103P.
Russo et al. (Thu,) studied this question.