Abstract
We report that minor planet 2004 CV50 displayed cometary activity in the form of a short, diffuse tail, first identified by volunteers of the Citizen Science program Active Asteroids, a NASA Partner program hosted on the Zooniverse online platform. The activity is present in three images, from UT 2020 February 15 and UT 2020 March 14, that were acquired with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro-Tololo Inter-American Observatory in Chile. We find that 2004 CV50 is most likely an active quasi-Hilda object rather than an active asteroid, despite 2004 CV50 having a Tisserand parameter with respect to Jupiter of 3.06.
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1. Introduction
Minor planets that display comet-like activity, such as tails or comae, teach us about the solar system's volatile distribution, including the origins of terrestrial water (Hsieh et al. 2015). Minor planet populations aside from comets are known to exhibit activity, decreasing the distinction between comet and asteroid (see Jewitt & Hsieh 2022). Several populations with active members are known, such as active asteroids and active quasi-Hilda objects. While active asteroids are typically found in the asteroid belt, active quasi-Hildas are minor planets on orbits similar to the Hilda asteroids, but quasi-Hildas are not in stable 3:2 interior mean-motion-resonance with Jupiter. Like Hildas and Jupiter Trojans, quasi-Hildas are often identified through dynamical integration, an added challenge for distinguishing between populations. Aside from comets, active small-body populations are rare, with fewer than 100 known among the 1.3 million minor planets identified to date.
2. Methods
To locate more of these elusive objects we created the Zooniverse-hosted Citizen Science program Active Asteroids, 17 a NASA Partner (Chandler 2022). We show volunteers images of minor planets we extracted from archival Dark Energy Camera (DECam) images and ask if they see evidence of activity, such as a tail or coma. We investigate volunteer-highlighted activity candidates by searching through astronomical image archives as well as conducting telescope follow-up, when possible.
For dynamical classification, we make use of the Tisserand parameter with respect to Jupiter,
where a and aJ are the semimajor axes of 2004 CV50 and Jupiter, e is orbital eccentricity, and i is inclination. Bodies with TJ < 3 are nominally cometary (Levison 1996), though TJ = 3.08 is also used (Jewitt et al. 2015). In practice, 3.05 < TJ < 3.10 is an ambiguous parameter space (Hsieh & Haghighipour 2016) that requires modeling to distinguish between, for example, Jupiter Family Comets and Hilda asteroids. We make use of the REBOUND N-body integration package (Rein & Liu 2012) for this purpose (Chandler et al. 2022; Oldroyd et al. 2023).
3. Results
Figure 1 shows 2004 CV50 with a diffuse tail on two different dates. On UT 2020 February 15 (one image), 2004 CV50 was at a heliocentric distance of rH = 1.68 au and a true anomaly angle of f = 343°. On UT 2020 March 14 (two images) 2004 CV50 was at rH = 1.66 au and f = 359°, essentially at perihelion. For both dates, the tail orientation was in the anti-motion direction. In February the anti-solar and anti-motion directions were coincident.
Figure 1. 2004 CV50 (at center) with a short, diffuse tail in these 120 s i-band DECam exposures (Prop. ID 2020A-0399, PI Zenteno, observer A. Diaz). Anti-motion (yellow arrow) and anti-solar (red-bordered black arrow) directions are indicated. The FOV is 32'' × 32'', with north up and east left. (a) UT 2020 February 15 at 08:47:22. (b) UT 2020 March 14 at 06:40:53. (c) UT 2020 March 14 at 06:44:38.
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2004 CV50 (a = 3.113 au, e = 0.438, i = 1.413°, perihelion distance q = 1.748 au, aphelion distance Q = 4.478 au; retrieved UT 2023 September 22 from JPL) has TJ = 3.061, typically indicating an asteroidal orbit. However, 2004 CV50 experiences close encounters with Jupiter, most recently 1.1 au on UT 2022 May 28, and our dynamical integrations indicate 2004 CV50 is an active quasi-Hilda. Along with 282P (Chandler et al. 2022), 2009 DQ118 (Oldroyd et al. 2023), and 2018 CZ18 (Trujillo et al. 2023), 2004 CV50 represents the fourth active quasi-Hilda identified via the Active Asteroids program.
Acknowledgments
Many thanks to Arthur and Jeanie Chandler for their ongoing support.
We thank Elizabeth Baeten (Belgium) for moderating the Active Asteroids forums. We thank our NASA Citizen Scientists who examined 2004 CV50: Al Lamperti (Royersford, USA), Angelina A. Reese (Sequim, USA), Dr. Brian Leonard Goodwin (London, UK), C. D'silva (Mumbai, India), Carl L. King (Ithaca, USA), Clara Garza (West Covina, USA), Dan Crowson (Dardenne Prairie, USA), Dawn Boles (Bakersfield , USA), Eric Fabrigat (Velaux, France), Graeme Aitken (Towen Mountain, Australia), Ivan A. Terentev (Petrozavodsk, Russia), Leah Mulholland (Peoria, Illinois, USA), Melina Thévenot (Belgium), Michele T. Mazzucato (Florence, Italy), Milton K. D. Bosch, MD (Napa, USA), Rosemary Billington (Wilmslow, UK), Somsikova Liudmila Leonidovna (Chirchik, Uzbekistan), Thorsten Eschweiler (Übach-Palenberg, Germany), Tiffany Shaw-Diaz (Dayton, USA), Tomasz Konecki (Warsaw, Poland), Virgilio Gonano (Udine, Italy), Washington Kryzanowski (Montevideo, Uruguay), and @WRSunset (Shaftesbury, UK).
Many thanks to Cliff Johnson (Zooniverse), Marc Kuchner (NASA), and Chris Lintott (Oxford) for their ongoing guidance.
This material is based upon work supported by the NSF Graduate Research Fellowship Program under grant No. 2018258765 and grant No. 2020303693. C.O.C., H.H.H., and C.A.T. acknowledge support from the NASA Solar System Observations program (grant 80NSSC19K0869). W.J.O. acknowledges support from NASA grant 80NSSC21K0114. This work was supported in part by NSF award 1950901. LINCC Frameworks is supported by Schmidt Futures, a philanthropic initiative founded by Eric and Wendy Schmidt, as part of the Virtual Institute of Astrophysics. Chandler acknowledges 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 (DES) collaboration. This research uses services or data provided by the Astro Data Archive at NSF's NOIRLab. Based on observations at Cerro Tololo Inter-American Observatory, NSF's NOIRLab (NOIRLab Prop. ID 2014B-0404; PI: D. Schlegel).
Facility: CTIO:4m (DECam) - .
Software: astropy (Robitaille et al. 2013), astrometry.net (Lang et al. 2010), REBOUND (Rein & Liu 2012) SAOImageDS9, SkyBot (Berthier et al. 2006).