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Properties of the Bare Nucleus of Comet 96P/Machholz 1

Eisner, N. L.; Knight, M. M.; Snodgrass, Colin; Kelley, M. S. P.; Fitzsimmons, A. and Kokotanekova, Rosita (2019). Properties of the Bare Nucleus of Comet 96P/Machholz 1. The Astronomical Journal, 157(5), article no. 186.

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We observed comet 96P/Machholz 1 on a total of nine nights before and after perihelion during its 2017/2018 apparition. Both its unusually small perihelion distance and the observed fragmentation during multiple apparitions make 96P an object of great interest. Our observations show no evidence of a detectable dust coma, implying that we are observing a bare nucleus at distances ranging from 2.3 to 3.8 au. Based on this assumption, we calculated its color and found average values of g'–r' = 0.50 ± 0.04, r'–i' = 0.17 ± 0.03, and </i>i'–z' = 0.06 ± 0.04. These are notably more blue than those of the nuclei of other Jupiter-family and long-period comets. Furthermore, assuming a bare nucleus, we found an equivalent nuclear radius of 3.4 ± 0.2 km with an axial ratio of at least 1.6 ± 0.1. The lightcurve clearly displays one large peak, one broad flat peak, and two distinct troughs, with a clear asymmetry that suggests that the shape of the nucleus deviates from that of a simple triaxial ellipsoid. This asymmetry in the lightcurve allowed us to constrain the nuclear rotation period to 4.10 ± 0.03 hr and 4.096 ± 0.002 hr before and after perihelion, respectively. Within the uncertainties, 96P's rotation period does not appear to have changed throughout the apparition, and we conclude a maximum possible change in rotation period of 130 s. The observed properties were compared to those of comet 322P and interstellar object 1I/'Oumuamua in an attempt to study the effects of close perihelion passages on cometary surfaces and their internal structure and the potential interstellar origin of 96P.

Item Type: Journal Item
Copyright Holders: 2019 The American Astronomical Society
ISSN: 1538-3881
Keywords: comets: individual; (96P/Machholz 1); data analysis methods; observational methods
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 61083
Depositing User: ORO Import
Date Deposited: 10 May 2019 10:23
Last Modified: 23 May 2019 20:48
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