Letter to the Editor

Refinement of the convex shape model and tumbling spin state of (99942) Apophis using the 2020–2021 apparition data

¹ Korea Astronomy and Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea
e-mail: hjlee@kasi.re.kr
² Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
³ Chungbuk National University, 1 Chungdae-ro, Seowon-gu, Cheongju, Chungbuk 28644, Korea
⁴ University of Science and Technology, 217, Gajeong-ro, Yuseong-gu, Daejeon 34113, Korea
⁵ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
⁶ Mt. Suhora Observatory, Pedagogical University, ul. Pochorążych 2, 30-084 Kraków, Poland
⁷ Las Cumbres Observatory, 6740 Cortona Drive Suite 102, Goleta, CA 93117, USA
⁸ Las Cumbres Observatory, School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
⁹ Asteroid Institute, 20 Sunnyside Ave, Suite 427, Mill Valley, CA 94941, USA
¹⁰ Department of Astronomy and the DIRAC Institute, University of Washington, 3910 15th Ave NE, Seattle, WA 98195, USA
¹¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eőtvős Loránd Research Network (ELKH), Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
¹² South African Astronomical Observatory, Cape Town 7925, South Africa
¹³ Department of Astronomy, University of Cape Town, Rondebosch 7701, South Africa
¹⁴ Kepler Institute of Astronomy, University of Zielona Góra, Lubuska 2, 65-265 Zielona Góra, Poland
¹⁵ Departamento de Sistema Solar, Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁶ National Youth Space Center, Goheung, Jeollanam-do 59567, Korea
¹⁷ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Planetary Research, 12489 Berlin, Germany
¹⁸ University of Occupational and Environmental Health, Japan, 1-1 Iseigaoka, Yahata, Kitakyusyu 807-8555, Japan
¹⁹ Planetary Exploration Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
²⁰ University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
²¹ Department of Physics, Adiyaman University, 02040 Adiyaman, Turkey
²² Dark Sky Observatory, Dept. of Physics and Astronomy, Appalachian State University, Boone, NC 28608, USA
²³ Akdeniz University, Department of Space Sciences and Technologies, 07058 Antalya, Turkey
²⁴ TÜBİTAK National Observatory, Akdeniz University Campus, 07058 Antalya, Turkey
²⁵ Astrophysics Application and Research Center, Adiyaman University, Adiyaman 02040, Turkey

Received: 28 February 2022
Accepted: 1 April 2022

Abstract

Context. The close approach of the near-Earth asteroid (99942) Apophis to Earth in 2029 will provide a unique opportunity to examine how the physical properties of the asteroid could be changed due to the Earth’s gravitational perturbation. As a result, the Republic of Korea is planning a rendezvous mission to Apophis.

Aims. Our aim was to use photometric data from the apparitions in 2020−2021 to refine the shape model and spin state of Apophis.

Methods. Using thirty-six 1- to 2-meter-class ground-based telescopes and the Transiting Exoplanet Survey Satellite, we carried out a photometric observation campaign throughout the 2020−2021 apparition. The convex shape model and spin state were refined using the light-curve inversion method.

Results. According to our best-fit model, Apophis is rotating in a short-axis mode with rotation and precession periods of 264.178 h and 27.38547 h, respectively. The angular momentum vector orientation of Apophis was found to be (275°, −85°) in the ecliptic coordinate system. The ratio of the dynamic moments of inertia of this asteroid was fitted to I_a : I_b : I_c = 0.64 : 0.97 : 1, which corresponds to an elongated prolate ellipsoid. These findings regarding the spin state and shape model can be used to both design the space mission scenario and investigate the impact of the Earth’s tidal force during close encounters.