Abstract
We present the discovery of cometary activity on 2018 OR as part of our Active Asteroids project, a NASA Partner Program fueled by Zooniverse Citizen Scientists. Volunteers found 2018 OR with a long, diffuse tail in archival images from the Dark Energy Camera on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Our team identified additional Canada–France–Hawaii–Telescope MegaCam and Zwicky Transient Facility archival data after classification by Citizen Scientists. Activity originating from 2018 OR and directed in the anti-solar and anti-velocity directions was visible in archival images between UT 2018 September 5–18. Our dynamical simulations indicate 2018 OR experiences close encounters with Jupiter over hundred-year timescales. The orbital period and dynamics suggest 2018 OR is a Jupiter Family Comet, and we recommend further observations from the community to reduce observational uncertainties and investigate activity patterns.
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1. Introduction
Jupiter Family Comets (JFCs) are a sub-class of comets with orbital periods <20 yr that cross Jupiter's orbit (Levison 1996). JFCs originate beyond Neptune and migrate through gravitational interactions with giant planets (Fraser et al. 2022), instructing our understanding of the solar system's dynamical interactions. JFCs can display a tail or coma, suggesting water ice sublimation (Jewitt & Hsieh 2022) and an opportunity to understand the solar system's water distribution.
2. Methods
The Active Asteroids project leverages volunteer participation to classify images of known minor planets as active or inactive, aiming to identify undiscovered activity in the Dark Energy Camera (DECam) public archive and increase the number of known active objects (Chandler et al. 2020, 2021, 2022; Chandler 2022). To date, over 8600 volunteers have contributed more than 7.1 million classifications. We conduct follow-up telescope observations and dynamical simulations to determine the dynamical class of promising candidates.
3. Results
Volunteers identified 2018 OR as active, and we identified 8 MegaCam, 9 Zwicky Transient Facility (Bellm et al. 2019), and 5 DECam archival images showing activity near perihelion. 2018 OR appeared with a tail in the anti-solar and anti-velocity directions, indicating volatile sublimation (Figure 1). Activity spans a true anomaly range from 6
39 < f < 2121 and heliocentric distances from 1.64–1.67 au. We note 122 additional images away from perihelion and without activity indicators among MegaCam, Zwicky Transient Facility (ZTF)
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(Bellm et al. 2019; Masci et al. 2019), DECam, OmegaCAM (VLT Survey Telescope; Paranal), and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; Haleakala) archives from 2003–2017.
Figure 1. 2018 OR (at center) with a tail in the anti-velocity (red-outlined black arrow) and anti-solar (yellow arrow) directions in 126'' × 126'' images. (a) UT 2018 September 5, 160 s GRI-band MegaPrime imager on the 3.6 m CFHT (proposal 18BH09, PI Wainscoat). (b) UT 2018 September 6, 46 s r-band DECam (Prop. ID 2014B-0404, PI Schlegel, observer Z. Slepian). (c) UT 2018 September 17, 30 s r-band ZTF camera (48'' Samuel Oschin telescope, Palomar).
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We identify 2018 OR (semimajor axis a = 3.53 au, eccentricity e = 0.54, inclination i = 205, perihelion distance q = 1.64 au, aphelion distance Q = 5.43 au, Tisserand parameter with respect to Jupiter TJ = 2.86; retrieved UT 2023 April 20, JPL Horizons) as an active JFC. Our simulations indicate close encounters with Jupiter (within 1 au) on hundred-year timescales, giving 2018 OR a 10% chance to migrate to the Centaur region (perihelion between Jupiter and Neptune) and a 5% chance to transition to a quasi-Hilda orbit (near the Hilda asteroids' resonance with Jupiter) in the next 1000 yr. We call for observations during 2018 OR's next perihelion passage (2025 March–June) to constrain orbital parameters, enabling more precise estimation of, e.g., close encounters, dynamical class, and activity patterns.
Acknowledgments
Many thanks to Arthur and Jeanie Chandler for their ongoing support.
We thank Elizabeth Baeten (Belgium) for moderating Active Asteroids forums, and our NASA Citizen Scientists who examined 2018 OR: Ethan Amado (Gilroy, USA), Elisabeth Baeten (Leuven, Belgium), Sarah Barratt (New Mills, UK), Simon Lund Sig Bentzen (Kolding, Denmark), Dawn Boles (Bakersfield, USA), Milton K. D. Bosch MD (Napa, USA), Dan Crowson (Dardenne Prairie, USA), Eric Fabrigat (Velaux, France), Thomas Fercho (Heidelberg, Germany), Erik Garrison (Salem, USA), Virgilio Gonano (Udine, Italy), J. Hamner (Windermere, USA), Marvin W. Huddleston (Mesquite, USA), Carl L. King (Ithica, USA), Tomasz Konecki (Warsaw, Poland), Washington Kryzanowski (Montevideo, Uruguay), Al Lamperti (Royersford, USA), Somsikova Liudmila Leonidovna (Chirchik, Uzbekistan), Michele T. Mazzucato (Florence, Italy), Julianne McLarney (Miami, USA), Zac Pujic (Brisbane, Australia), Angelina A. Reese, (Sequim, USA), Stikhina Olga Sergeevna (Tyumen, Russia), Tiffany Shaw-Diaz (Dayton, USA), José A. da Silva Campos (Portugal), Ivan A. Terentev (Petrozavodsk, Russia), Monisha Uriti (Puyallup, USA), @graham_d (Hemel Hempstead, UK).
A special thanks to the Active Asteroids project Superclassifiers: @EEZuidema (Driezum, Netherlands), @graham_d (Hemel Hempstead, UK), Angelina A. Reese (Sequim, USA), Antonio Pasqua (Catanzaro, Italy), Carl L. King (Ithaca, USA), Dan Crowson (Dardenne Prairie, USA), Eric Fabrigat (Velaux, France), Henryk Krawczyk (Czeladż Poland), Marvin W. Huddleston (Mesquite, USA), Robert Zach Moseley (Worcester, USA), Thorsten Eschweiler (Übach-Palenberg, Germany), and Washington Kryzanowski (Montevideo, Uruguay). Many thanks to Cliff Johnson (Zooniverse), Chris Lintott (Oxford), and Marc Kuchner (NASA) for ongoing guidance.
This material is based upon work supported by the NSF Graduate Research Fellowship Program under grant No. 2018258765 and grant No. 2020303693. W.J.O. and C.A.T. acknowledge support from NASA grant 80NSSC21K0114. C.O.C., H.H.H., and C.A.T. acknowledge support from NASA grant 80NSSC19K0869. This work was supported in part by NSF award 1950901. This research received support through the generosity of Eric and Wendy Schmidt by recommendation of the Schmidt Futures program. Chandler and Sedaghat acknowledge support from the DIRAC Institute in the Department of Astronomy at the University of Washington. The DIRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences, and the Washington Research Foundation. Computational analyses were run on Northern Arizona University's Monsoon computing cluster, funded by Arizona's Technology and Research Initiative Fund.
This research has made use of NASA's Astrophysics Data System, and data and/or services provided by the International Astronomical Union's Minor Planet Center.
This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey collaboration. Based on observations obtained with MegaPrime/MegaCam, a joint project of Canada–France–Hawaii–Telescope (CFHT) and CEA/DAPNIA, at the CFHT which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. The observations at the Canada–France–Hawaii Telescope were performed with care and respect from the summit of Maunakea which is a significant cultural and historic site. This research uses services or data provided by the Astro Data Archive at NSF's NOIRLab.
Facilities: CTIO: 4 m (DECam) - , CFHT 3.58 m (MegaCam) - , IRSA (ZTF) PO: 1.2 m - , STScI: 1.8 m (Pan-STARRS1) - , VST 2.65 m (OmegaCAM) - .
Software: astrometry.net (Lang et al. 2010), JPL Horizons (Giorgini et al. 1996), REBOUND (Rein & Liu 2012), SkyBot (Berthier et al. 2006).
Footnotes
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Data can be obtained at IRSA (IRSA 2022).