Abstract
We report the discovery of cometary activity emanating from minor planet 2015 VP51 outbound from its recent perihelion passage. The activity, in the form of a diffuse tail, was first identified by volunteers of our Citizen Science program Active Asteroids, a NASA Partner program hosted on the Zooniverse platform. This discovery was aided by the recently implemented TailNet artificial intelligence assistant which filters out images with a low likelihood of showing cometary activity. The tail is present in nine images of 2015 VP51 from the Dark Energy Camera and OmegaCAM between UT 2015 August 2 and UT 2015 October 18. We classify 2015 VP51 as a Jupiter-family comet based on its Tisserand parameter with respect to Jupiter TJ = 2.931.
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1. Introduction
Comets are small solar system bodies known for tails and comae usually caused by volatile sublimation. Therefore, the abundance and distribution of these active objects are important for understanding the past and present distribution and transport of volatiles in the solar system. One class of comets, the Jupiter-family comets (JFCs), are defined as comets with a Tisserand parameter with respect to Jupiter 2 < TJ < 3 (H. F. Levison & M. J. Duncan 1994). JFCs likely originate from the Kuiper Belt and thus contain material from the early stages of the solar system's formation (H. F. Levison & M. J. Duncan 1997).
2. Methods
Active Asteroids 18 is our NASA Partner Citizen Science program intended to discover cometary activity from minor planets not previously known to be active (C. O. Chandler et al. 2024b). First, we search the public archive of the Dark Energy Camera (DECam), an instrument on the Víctor M. Blanco 4 m Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile, for exposures containing known minor planets (C. O. Chandler et al. 2018). To enhance volunteer experience, we developed a convolutional neural network, TailNet, which assigns each image a likelihood that the object does not show activity (the network is trained primarily on negative classifications) (C. O. Chandler et al. 2024a; J. A. DeSpain et al. 2024; N. Sedaghat et al. 2024). We filter out the images that TailNet determines to be unlikely to show activity and pass these pre-screened cutouts to the volunteers. We further investigate objects consistently classified as active by volunteers with archival searches and telescope observations.
3. Results
Active Asteroids volunteers identified 2015 VP51 as showing activity in one DECam image from UT 2015 October 18. We then searched additional public archives for images potentially containing 2015 VP51, finding eight more exposures showing activity (Figure 1): four VLT Survey Telescope (VST; M. Arnaboldi et al. 1998) OmegaCAM (K. Kuijken 2011) images from UT 2015 August 2 (true anomaly angle f = 38°), three DECam images from UT 2015 September 13 (f = 50°), and one additional DECam image from the same night as the image identified by project volunteers: UT 2015 October 18 (f = 60°). This gives us nine total images of 2015 VP51 between UT 2015 August 2 and October 18 showing activity.
Figure 1. 2015 VP51 is at the center of these 63'' × 63'' images; North is up, East left. Red outlined black arrows and yellow filled arrows indicate the anti-motion and anti-solar directions, as project on the sky. (a) UT 2015 August 2: Co-addition of 3 × 240 s i-band exposures captured with the OmegaCAM instrument on the 2.6 m VLT Survey Camera (VST) atop Cerro Paranal (Chile) as part of the Kilo-Degree Survey (KiDS; K. Kuijken et al. 2019). (b) UT 2015 September 13: Co-addition of 3 (1 × 90 s g-band, 1 × 90 s r-band, 1 × 90 s i-band) DECam images (Prop. ID 2012B-0001, PI Frieman, observers Josh Frieman, Devon Hollowood, Ofer Lahav, Alex Kim). (c) UT 2015 October 18: Co-addition of 2 (1 × 90 s g-band, 1 × 90 s r-band) DECam images (Prop. ID 2012B-0001, PI Frieman, observers William Wester, Lucas Beaufore, Ann Elliott).
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With a Tisserand parameter with respect to Jupiter of TJ = 2.931, we classify 2015 VP51 (semimajor axis a = 3.187 au, eccentricity e = 0.309, inclination i = 29
3, perihelion distance q = 2.20 au, aphelion distance Q = 4.171 au) as a JFC (see Section 1). The activity occurred just after perihelion, (38° < f < 60°), consistent with sublimation-driven activity and the corresponding presence of volatiles. 2015 VP51 will pass perihelion again on UT 2026 August 23 at which time it will have an apparent magnitude of V = 20.7, comparable to the images in which we identified activity (Figure 1). Observations of 2015 VP51 showing activity during another perihelion passage would reinforce that the activity is caused by sublimation rather than another process like impact or rotational disruption.
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 2015 VP51: Andreas Hahn (Berlin, Germany), Antonio Pasqua (Catanzaro, Italy), Henryk Krawczyk (Czeladż Poland), Jose A. da Silva Campos (Portugal), Kayla Jessen (Calgary, Canada), Kim Donghyeon (Cheonan, Korea), Mathieu Moreau (La Châtre, France), Michele T. Mazzucato (Florence, Italy), Milton K. D. Bosch MD (Napa, USA), Tiffany Shaw-Diaz (Dayton, USA), and @voyager1977 (Manchester, UK).
A special thanks to the Active Asteroids Superclassifiers: Angelina A. Reese (Sequim, USA), Antonio Pasqua (Catanzaro, Italy), Carl L. King (Ithaca, USA), Dan Crowson (Dardenne Prairie, USA), @EEZuidema (Driezum, Netherlands), Eric Fabrigat (Velaux, France), @graham_d (Hemel Hempstead, UK), Henryk Krawczyk (Czeladż Poland), Marvin W. Huddleston (Mesquite, USA), Robert Zach Moseley (Worcester, USA), Thorsten Eschweiler (Übach-Palenberg, Germany), and Washington Kryzanowski (Montevideo, Uruguay). Thanks to Cliff Johnson (Zooniverse), Chris Lintott (Oxford), and Marc Kuchner (NASA) for ongoing Citizen Science guidance.
This work was supported in part by NASA grants 80NSSC19K0869 and 80NSSC21K0114, NSF GRFP grant Nos. 2018258765 and 2020303693, and NSF award 1950901. This research received support through Schmidt Sciences. M.K.F, C.O.C, and N.S. 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.
Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 177.A-3016, 177.A-3017, 177.A-3018 and 179.A-2004, and on data products produced by the KiDS consortium. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration.
Facilities: CTIO:4m (DECam) - , VLT:VST (OmegaCAM) - .
Software: astrometry.net (D. Lang et al. 2010).