Near-Earth asteroid (3200) Phaethon: Characterization of its orbit, spin state, and thermophysical parameters

¹ Centre National d’Études Spatiales, 2 place Maurice Quentin, 75039 Paris Cedex 01, France
e-mail: hanus.home@gmail.com
² Laboratoire Lagrange, UMR 7293, Université de la Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, Bvd de l’Observatoire, CS 34229, 06304 Nice Cedex 04, France
³ Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic
⁴ Astronomical Institute, Academy of Sciences of the Czech Republic, Fričova 1, 25165 Ondřejov, Czech Republic
⁵ Earth and Planetary Science Department, Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996, USA
⁶ Département d’Astrophysique, Géophysique et Océanographie, Université de Liège, Allèe du Six Août 17, 4000 Liège, Belgium
⁷ Badlands Observatory, 12 Ash Street, PO Box 37, Quinn, SD 57775, USA
⁸ Modra Observatory, Department of Astronomy, Physics of the Earth, and Meteorology, FMPI UK, 84248 Bratislava, Slovakia
⁹ Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822, USA
¹⁰ Instituto de Astrofísica de Canarias (IAC), C Vía Láctea s/n, 38205 La Laguna, Spain
¹¹ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹² Planetary Science Institute, 1700 East Fort Lowell Road, Tucson, AZ 85719, USA
¹³ 446 Sycamore Ave., Eaton, CO 80615, USA

Received: 7 April 2016
Accepted: 13 May 2016

Abstract

Context. The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is at only 0.14 au and is associated with the Geminid meteor stream.

Aims. We aim to use all available disk-integrated optical data to derive a reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo.

Methods. We applied the convex inversion method to the new optical data obtained by six instruments and to previous observations. The convex shape model was then used as input for the thermophysical modeling. We also studied the long-term stability of Phaethon’s orbit and spin axis with a numerical orbital and rotation-state integrator.

Results. We present a new convex shape model and rotational state of Phaethon: a sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319°, −39°) with a 5° uncertainty. Moreover, we derive its size (D = 5.1 ± 0.2 km), thermal inertia (Γ = 600 ± 200 J m^–2 s^–1/2 K^–1), geometric visible albedo (p_V = 0.122 ± 0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during the past several thousand years is not connected to a specific area on the surface, which implies non-preferential heating.