Probable Detection of Water Ice in the Coma of the Inbound Long-period Comet C/2017 K2 (PanSTARRS)

Abstract

Abstract We present near-infrared reflectance spectra from 0.7 to 2.5 μm taken 2021 April 30 at the NASA Infrared Telescope Facility that show strong evidence for water ice within the coma of comet C/2017 K2 (PanSTARRS) at a heliocentric distance of R H = 6.488 au. This object has likely been active since ∼35 au inbound and this provides a key piece of information to interpreting these early observations, understanding its dust properties, and assessing its overall volatile inventory and release mechanisms. A preliminary spectral model is best-fit with a volume fraction of ice of ∼14% assuming that the refractory and volatile materials are mixed intimately. More sophisticated modeling and a deeper analysis of these data will be presented in a manuscript to be submitted later this year.