2021 STELLAR OCCULTATION OBSERVATIONS OF ASTEROID (3200) PHAETHON FOR THE
DESTINY+ FLYBY. T. Arai1, F. Yoshida2,1, T. Hayamizu3,4, H. Akitaya1, T. Okamoto1, H. Noda5, M. Ishiguro6, S.
Urakawa7, T. Horaguchi8, M.-Y. Yamamoto9, G. Hashimoto10, S. Matsuura11, S. Marshall12, and the DESTINY+Occultation Observation Team. 1Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, Japan (tomoko.arai@it-chiba.ac.jp), 2 University of Occupational & Environmental Health, Fukuoka, Japan, 3SagaHoshizora Astronomical Center, Japan, 4Japan Occultation Information Network (JOIN), Japan, 5National Astronomical Observatory of Japan, Japan, 6Seoul National University, South Korea, 7Japan Spaceguard Association,Japan, 8National Museum of Nature and Science, Tokyo, Japan, 9Kochi University of Technology, Kochi, Japan,10Okayama University, Okayama, Japan, 11Kwansei Gakuin University, Hyogo, Japan, 12Arecibo Observatory &University of Central Florida, USA.
Introduction: DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary
voYage, Phaethon fLyby and dUst Science) is a joint
mission of technology demonstration and scientificobservation, which will be launched in 2024 and flyby
asteroid (3200) Phaethon in January, 2028 [1]. Phaethon is a parent body of the Geminids meteor shower[2, 3]. Asteroid 2005 UD is likely a break-up bodyfrom Phaethon [4]. Phaethon still actively ejects dust
during every perihelion passage [5-9]. Phaethon passed
0.07 au from the Earth on December 16, 2017, whichis the closest approach since 1974 and until 2093. During this apparition, global astronomical observation
campaign of Phaethon was conducted [10], including
optical, spectroscopic, polarimetric and radar observation with ground and space-based telescopes [11-23].
There were large differences in the size estimate between two-dimensional delay-Doppler radar images ofArecibo (6 km, dia.) [14] and thermophysical modelling results of observations from NEOWISE mission(4.6 km, dia.) [23]. The variable size estimates yield arange of albedo estimate of 0.09-0.16 [e.g. 15, 23]. To
determine the size of Phaethon independently, observations of stellar occultation were conducted across theglobe [24]. The best size information came from theJuly 29, 2019 event in the southwest U.S. [25]. The
size and shape determination have been done based on
the above occultation observation outcome combinedwith light curve and radar observation [26]. Yet, theshape model has 10-20% uncertainty [26] and thus
further stellar occultation observation is needed to decrease the uncertainty. Here, we report observation
results of stellar occultation by Phaethon in Japan andSouth Korea on October 13, 2021.
Occultation prediction: Predictions were madebased on the new Gaia EDR3 catalog [27, 28]. The
predicted occultation path in Japan on October 13,
2021 is shown in Fig. 1.
Observation equipments: Due to faint stars andshort duration for occultation in most events, large
telescopes of 20-30 cm coupled with GPS video-rate
recording. QHY174M-GPS cameras with CMOS detector and integrated GPS receiver for accurate time
tagging of images were used. The readout time wasnegligible.

Results: Total 35 stations with total 71 observers
were deployed from the southwestern part of the mainisland of Japan to the southern part of South Korea.
The weather was good at most of the observation sites.
The observation was a huge success. Of the 35 observation sites, positive occultation was recorded at 17sites and negative occultation at 7 sites. The reduction
profile is shown in Fig. 2.
Size determination: The size of Phaethon derived
from the October 13 observation is 6.13±0.05 km,4.40±0.06 km. The shape indicated by the result ismore flattened in both polar regions than previously
estimated (Fig. 3). The 3D shape model of Phaethon iscurrently being updated with the observation result.
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Gaia Data Release 2. Summary of the contents andsurvey properties.

Fig 1. Predicted occultation paths on Oct. 13, 2021.
(generated by T. Hayamizu from OCCULT4.12.13.0)

Fig. 2 The reduction profile of Oct. 13 observation.
(generated by T. Hayamizu)

Fig. 3 Reduction profile of Fig. 2 onto the previous
shape model. (generated by T. Hayamizu)