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Dust Evolution in the Coma of Distant, Inbound Comet C/2017 K2 (PANSTARRS)

Zhang, Qicheng and Kolokolova, Ludmilla and Ye, Quanzhi and Vissapragada, Shreyas (2022) Dust Evolution in the Coma of Distant, Inbound Comet C/2017 K2 (PANSTARRS). Planetary Science Journal, 3 (6). Art. No. 135. ISSN 2632-3338. doi:10.3847/psj/ac6d58.

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C/2017 K2 (PANSTARRS) is an Oort Cloud comet previously observed to be active at heliocentric distances r > 20 au on what is likely its first passage through the inner solar system. We observed the comet on 2021 March 19–20 at r = 6.82 au preperihelion and 8.°35 phase angle with the Hubble Space Telescope (HST), and obtained high spatial resolution photometry and polarimetry mapping the properties of dust over the coma prior to the onset of water ice sublimation activity on the nucleus. We found clear radial gradients in the color and polarization of the coma: the F475W–F775W (g' - i') reflectance slope increased from ∼4.5% per 100 nm within ∼10,000 km of the nucleus up to ∼7% per 100 nm by ∼50,000 km, while the negative polarization in F775W (i') strengthened from about −2% to −3.5% over the same range. The radial intensity profiles moreover strongly deviate from profiles simulated for stable dust grains. Near-infrared imagery obtained with the Palomar Hale Telescope on 2021 May 18 at r = 6.34 au revealed a continued absence of micron-sized grains in the tail, but showed no clear spatial gradient in JHKₛ colors. The observed patterns collectively appear consistent with the inner coma being optically dominated by sublimating, micron-sized water ice grains, unlike the tail of more stable, millimeter-sized grains. Finally, we evaluated these results alongside other Oort Cloud comets, and found in a reanalysis of HST observations of C/2012 S1 (ISON) that the near-nucleus polarimetric halo reported for that comet is likely an observational artifact.

Item Type:Article
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URLURL TypeDescription Paper
Zhang, Qicheng0000-0002-6702-191X
Kolokolova, Ludmilla0000-0002-9321-3202
Ye, Quanzhi0000-0002-4838-7676
Vissapragada, Shreyas0000-0003-2527-1475
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 September 22; revised 2022 April 14; accepted 2022 May 4; published 2022 June 7. We thank Michael Leveille and Marco Chiaberge for observing support on the Hubble Space Telescope, and Joel Pearman for support on the Hale Telescope at Palomar Observatory. We also thank the anonymous referees for their comments and suggestions that helped us improve this manuscript. This work is based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Support for program number HST-GO-16214 was provided through a grant from the STScI under NASA contract NAS5-26555. This research has also made use of observations from the Hale Telescope at Palomar Observatory, which is owned and operated by Caltech and administered by Caltech Optical Observatories. This research has made use of data and/or services provided by the International Astronomical Union's Minor Planet Center and by the Jet Propulsion Laboratory's Solar System Dynamics group. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. S.V. was supported by an NSF Graduate Research Fellowship and the Paul & Daisy Soros Fellowship for New Americans. Facilities: Hale (WIRC) - , HST (ACS). - Software: ACSTools (Lim et al. 2020), Astropy (Astropy Collaboration et al. 2018), Matplotlib (Hunter 2007), NumPy (Van Der Walt et al. 2011), Photutils (Bradley et al. 2016), STWCS (Dencheva et al. 2011), Tiny Tim (Krist et al. 2011).
Funding AgencyGrant Number
Gaia Multilateral AgreementUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Paul and Daisy Soros Fellowships for New AmericansUNSPECIFIED
Subject Keywords:Coma dust; Comae; Comets; Long period comets
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Coma dust (2159); Comae (271); Comets (280); Long period comets (933)
Record Number:CaltechAUTHORS:20220608-848766000
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Official Citation:Qicheng Zhang et al 2022 Planet. Sci. J. 3 135
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115073
Deposited By: George Porter
Deposited On:14 Jun 2022 15:42
Last Modified:14 Jun 2022 15:42

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