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Modeling Ice & Dust in C/2017 K2 (PanSTARRS)’s Coma

Presentation #109.01 in the session Dusty and Icy Cometary Comae.

Published onOct 20, 2022
Modeling Ice & Dust in C/2017 K2 (PanSTARRS)’s Coma

C/2017 K2 (PanSTARRS) is an inbound long-period comet that has been active since 24 AU and likely as far out as 35 AU (Jewitt et al., 2017, 2021) well outside the water ice line. Near-Infrared (0.7–2.4 microns) spectroscopic observations were obtained with the SpeX instrument at the NASA Infrared Telescope Facility (IRTF) on 2021 April 30 at a heliocentric distance of ~6.5 AU that showed clear signs of water ice (Kareta et al., 2021) in its coma, which led us to begin a campaign to monitor K2 with the NIHTS instrument on the Lowell Discovery Telescope (LDT), including observations in March and June 2022, to further characterize the initially detected water ice. The SpeX data shows strong water ice absorption features at 1.5 and 2.0 microns with an overall red slope while the NIHTS data preliminarily shows much weaker ice bands. We ran several different spectral models utilizing a Markov Chain Monte Carlo approach to characterize the dust and ice in the coma. We found that several different combinations of parameters, such as Hapke vs. Mie scattering and linear vs. intimate mixing, resulted in different models that fit the data similarly well with different ice fractions ranging from ~7% to ~14%. Some of our models did, however, prefer large dust grains and small water ice grains, in line with interpretations of recent Hubble observations (Zhang et al., 2022). We discuss the most interesting of these models and compare them to those of other comets to better determine what causes comets to have ice in their comae. We also discuss our plans to model the NIHTS observations and collect more observations in the future.

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