Observational Characterization of Main-belt Comet and Candidate Main-belt Comet Nuclei

Henry H. Hsieh, Marco Micheli, Michael S.P. Kelley, Matthew M. Knight, Nicholas A. Moskovitz, Jana Pittichová, Scott S. Sheppard, Audrey Thirouin, Chadwick A. Trujillo, Richard J. Wainscoat, Robert J. Weryk, Quanzhi Ye

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4 Scopus citations


We report observations of nine main-belt comets (MBCs) or candidate MBCs, most of which were obtained when the targets were apparently inactive. We find effective nucleus radii (assuming albedos of p V = 0.05 ± 0.02) of r n = (0.24 ± 0.05) km for 238P/Read, r n = (0.9 ± 0.2) km for 313P/Gibbs, r n = (0.6 ± 0.1) km for 324P/La Sagra, r n = (1.0 ± 0.2) km for 426P/PANSTARRS, r n = (0.5 ± 0.1) km for 427P/ATLAS, r n < (0.3 ± 0.1) km for P/2016 J1-A (PANSTARRS), r n < (0.17 ± 0.04) km for P/2016 J1-B (PANSTARRS), r n ≤ (0.5 ± 0.2) km for P/2017 S9 (PANSTARRS), recently redesignated 455P/PANSTARRS, and r n = (0.4 ± 0.1) km for P/2019 A3 (PANSTARRS). We identify evidence of activity in observations of 238P in 2021, and find similar inferred activity onset times and net initial mass-loss rates for 238P during perihelion approaches in 2010, 2016, and 2021. P/2016 J1-A and P/2016 J1-B are also found to be active in 2021 and 2022, making them collectively the tenth MBC confirmed to be recurrently active near perihelion and therefore likely to be exhibiting sublimation-driven activity. The nucleus of 313P is found to have colors of g ′ − r ′ = 0.52 ± 0.05 and r ′ − i ′ = 0.22 ± 0.07 , consistent with 313P being a Lixiaohua family member. We also report nondetections of P/2015 X6 (PANSTARRS), where we conclude that its current nucleus size is likely below our detection limits (r n ≲ 0.3 km). Lastly, we find that of 17 MBCs or candidate MBCs for which nucleus sizes (or inferred parent body sizes) have been estimated, >80% have r n ≤ 1.0 km, pointing to an apparent physical preference toward small MBCs, where we suggest that Yarkovsky-O’Keefe-Radzievskii-Paddack spin-up may play a significant role in triggering and/or facilitating MBC activity.

Original languageEnglish (US)
Article number43
JournalPlanetary Science Journal
Issue number3
StatePublished - Mar 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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