(155140) 2005 UD and (3200) Phaethon*
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The Planetary Science Journal, 1:15 (15pp), 2020 June https://doi.org/10.3847/PSJ/ab8e45 © 2020. The Author(s). Published by the American Astronomical Society. New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon* Maxime Devogèle1 , Eric MacLennan2, Annika Gustafsson3 , Nicholas Moskovitz1 , Joey Chatelain4, Galin Borisov5,6, Shinsuke Abe7, Tomoko Arai8, Grigori Fedorets2,9, Marin Ferrais10,11,12, Mikael Granvik2,13 , Emmanuel Jehin10, Lauri Siltala2,14, Mikko Pöntinen2, Michael Mommert1 , David Polishook15, Brian Skiff1, Paolo Tanga16, and Fumi Yoshida8 1 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA; [email protected] 2 Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland 3 Department of Astronomy & Planetary Science, Northern Arizona University, P.O. Box 6010, Flagstaff, AZ 86011, USA 4 Las Cumbres Observatory, CA, USA 5 Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK 6 Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussèe Blvd., Sofia BG-1784, Bulgaria 7 Aerospace Engineering, Nihon University, 7-24-1 Narashinodai, Funabashi, Chiba 2748501, Japan 8 Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Japan 9 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK 10 Space sciences, Technologies & Astrophysics Research (STAR) Institute University of Liège Allée du 6 Août 19, B-4000 Liège, Belgium 11 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille, France 12 Space sciences, Technologies, France 13 Division of Space Technology, LuleåUniversity of Technology, Box 848, SE-98128 Kiruna, Sweden 14 Nordic Optical Telescope, Apartado 474, E-38700 S/C de La Palma, Santa Cruz de Tenerife, Spain 15 Faculty of Physics, Weizmann Institute of Science, 234 Herzl St. Rehovot 7610001, Israel 16 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, CS34229, F-06304 Nice Cedex 4, France Received 2020 January 29; revised 2020 April 25; accepted 2020 April 27; published 2020 May 20 Abstract In 2018, the near-Earth object (155140) 2005 UD (hereafter UD) experienced a close fly by of the Earth. We present results from an observational campaign involving photometric, spectroscopic, and polarimetric observations carried out across a wide range of phase angles (0°.7–88°). We also analyze archival NEOWISE observations. We report an absolute magnitude of HV=17.51±0.02 mag and an albedo of pV=0.10±0.02. UD has been dynamically linked to Phaethon due their similar orbital configurations. Assuming similar surface properties, we derived new estimates for the diameters of Phaethon and UD of D=5.4±0.5 km and D=1.3±0.1 km, respectively. Thermophysical modeling of NEOWISE data suggests a surface thermal inertia +120 – – of G = 300-110 and regolith grain size in the range of 0.9 10 mm for UD and grain sizes of 3 30 mm for Phaethon. The light curve of UD displays a symmetric shape with a reduced amplitude of Am(0)=0.29 mag and increasing at a linear rate of 0.017 mag/° between phase angles of 0° and ∼25°. Little variation in light-curve morphology was observed throughout the apparition. Using light-curve inversion techniques, we obtained a sidereal rotation period P=5.235±0.005 hr. A search for rotational variation in spectroscopic and polarimetric properties yielded negative results within observational uncertainties of ∼10% μm−1 and ∼16%, respectively. In this work, we present new evidence that Phaethon and UD are similar in composition and surface properties, strengthening the arguments for a genetic relationship between these two objects. Unified Astronomy Thesaurus concepts: Near-Earth objects (1092); CCD observation (207); Astronomical techniques (1684); Photometry (1234); Polarimetry (1278); Spectroscopy (1558) 1. Introduction near-Earth space suggests that any dynamical correlation between the two bodies would not be maintained for more The Apollo-type near-Earth object (NEO; 155140) 2005UD than a few thousand years (Schunová et al. 2014). (hereafter UD) was discovered by the Catalina Sky Survey in (3200)Phaethon is an intriguing NEO both in terms of 2005 (Christensen et al. 2005, MPEC 2005-U22). Ohtsuka ( ) ( ) orbital elements and physical properties. It displays a highly et al. 2006 and Jewitt & Hsieh 2006 showed that it displays eccentric orbit (e=0.89) associated with a very low perihelion orbital properties and photometric colors similar to the well- ( = ) ( ) distance q 0.14 au . Its close approaches to the Sun suggest known NEO 3200 Phaethon, suggesting a genetic relation- that its surface experiences large diurnal and seasonal ship between the two. However, more recent dynamical temperature variations. Phaethon has also been linked to the analyses have raised questions regarding a formal link Geminid meteor stream (Whipple 1983; Ryabova 2012). ( ) Ryabova et al. 2019 , though the chaotic nature of orbits in However, very low levels of activity centered on just a few * days around perihelion are too low to explain the observed Partially based on data collected with 2 m RCC telescope at Rozhen National Geminid meteor flux (Li & Jewitt 2013). Phaethon is also Astronomical Observatory. considered to be the parent of three other meteor streams, all belonging to the Geminid meteor complex. These streams Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further correspond to the intersection of the orbit of the Earth with that distribution of this work must maintain attribution to the author(s) and the title of Phaethon’s at different epochs (Babadzhanov & Obrubov of the work, journal citation and DOI. 1987; Jakubík & Neslušan 2015). However, one of these 1 The Planetary Science Journal, 1:15 (15pp), 2020 June Devogèle et al. Table 1 D∼5 km. These discrepancies in albedo and size could result Osculating Orbital Elements of Phaethon and Its Two Companions 2005 UD from Phaethon having an uncommon or inhomogeneous and 1999 YC at Epoch 59,000.0 MJD Obtained with the JPL Horizons Service surface. Variation of the linear degree of polarization was Phaethon 2005 UD 1999 YC indeed observed as a function of the rotation phase suggesting ( a ( ) that the surface of Phaethon is not uniform Borisov et al. 2018; au 1.271 1.275 1.422 ) e 0.890 0.872 0.831 Devogèle et al. 2018 . i (°) 22.259 28.668 38.232 The spectrum of Phaethon displays a blue slope compatible ω (°) 265.2 19.7 64.8 with a B-type taxonomy in the Bus and Binzel (visible; Bus & Ω (°) 322.2 207.6 156.4 Binzel 2002) and Bus-DeMeo (NIR inclusive; DeMeo et al. 2009) systems. Spectral variation with rotation was found by Kareta et al. (2018), however, with marginal significance. Phaethon is the target of the Japanese Aerospace Exploration streams, the daytime Sextantids, seems to be more closely Agency’s Demonstration and Experiment of Space Technology ( ) related to UD than it is to Phaethon Ohtsuka et al. 2005, 2006 . for INterplanetary voYage Phaethon fLyby dUSt science Phaethon and UD are also dynamically associated with ( +) ( ) ( DESTINY mission. It is planned to launch in 2022 and another asteroid, 225416 1999 YC Kasuga & Jewitt 2008, will perform a high-speed fly by of Phaethon (Arai et al. 2018). ) + hereafter YC . However, while Phaethon and UD display A possible mission extension for DESTINY would be a flyby photometric colors and spectra indicative of a blue slope and a of UD. As a result, ground-based campaigns of telescopic B-type spectral classification, YC shows redder colors more observations focused on both objects have been organized for consistent with a C-type classification (Kasuga & Jewitt 2008). mission preparation purposes. In this work, we present Table 1 compares the orbital elements of the parent body photometric, spectroscopic, and polarimetric results for UD Phaethon with its two putative family members UD and YC. and discuss its relation with its suspected parent body, Though the current osculating orbital elements of Phaethon and UD are different, particularly the longitude of ascending node Phaethon. and the argument of perihelion angles, they display similar In the next section, we present a summary of our secular variations in orbital elements with a time lag observations of UD in photometry, spectroscopy, and polari- Δt∼4600 yr (Ohtsuka et al. 2006). This means that ∼4600 metry. We also detail the thermal data used from NEOWISE. yr ago, the orbital elements of Phaethon were similar to those For each technique, the data acquisition and reduction of UD today. In the case of YC, the semimajor axis is procedures are detailed. Section 3 is devoted to discussion of significantly different from that of Phaethon and UD. If YC is the results from each technique. From the photometry, we genetically related to Phaethon and UD, these differences can discuss the rotation period and pole determination of UD. As only be explained if the orbit of YC was perturbed during a our observations span a large range of phase angles, we also close planetary encounter (Ohtsuka et al. 2008). If these three determined the photometric phase curve, estimation of the asteroids are actually related, their formation mechanism is absolute H magnitude, size of UD, and the variation of the unclear and could involve YORP spin-up and fission (Pravec amplitude as a function of the phase angle. The visible et al. 2010), impacts with other asteroids, or thermally driven spectroscopy allowed us to determine the taxonomic type of separation during a perihelion passage (Granvik et al. 2016). UD and compare it with the spectrum of Phaethon. Polarimetric Phaethon has been the subject of many studies to understand observations allowed for characterization of the phase-polar- its physical properties.