[P-PS03] Small Solar System Bodies: New perspectives on the origin and evolution of the Solar System

[PPS03-13] Current status of DESTINY+ project and science

*Tomoko Arai¹, Masanori Kobayashi¹, Ko Ishibashi¹, Fumi Yoshida², Hiroshi Kimura¹, Takayuki Hirai¹, Peng Hong¹, Takaya Okamoto¹, Koji Wada¹, Hiroki Senshu¹, Manabu Yamada¹, Hiroshi Akitaya¹, Ralf Srama³, Harald Kruger⁴, Masateru Ishiguro⁵, Tomoki Nakamura⁶, Sho Sasaki⁷, Hikaru Yabuta⁸, Junichi Watanabe⁹, Takashi Ito⁹, Takafumi Ootsubo⁹, Katsuhito Ohtsuka¹⁰, Jin Beniyama¹¹, Tomokatsu Morota¹¹, Takashi Mikouchi¹¹, Shogo Tachibana¹¹, Takahiro Hiroi¹², Tomohiko Sekiguchi¹³, Shinsuke Abe¹⁴, Seitaro Urakawa¹⁵, Shuji Matsuura¹⁶, Motoo Ito¹⁷, Akira Yamaguchi¹⁸, Takaaki Noguchi¹⁹, Mutsumi Komatsu²⁰, Keiko Nakamura-Messenger²¹, Eri Tatsumi²², Naru Hirata²³, Hirohide Demura²³, Goro Komatsu²⁵, Hidehiro Kaneda²⁴, Sean Marshall²⁶, Hajime Yano²⁷, Makoto Yoshikawa²⁷, Naoya Ozaki²⁷, Takayuki Yamamoto²⁷, Hiroyuki Toyota²⁷, Kazutaka Nishiyama²⁷, Hiroshi Imamura²⁷, Takashi Takashima²⁷ (1.Planetary Exploration Research Center, Chiba Institute of Technology, 2.University of Occupational and Environmental Health, 3.University of Stuttgart, 4.Max Planck Institute for Solar System Research, 5.Seoul National University, 6.Tohoku University, 7.Osaka University, 8.Hiroshima University, 9.National Astronomical Observatory of Japan, 10.Tokyo Meteor Network, 11.The University of Tokyo, 12.Brown University, 13.Hokkaido University of Education, 14.Nihon University, 15.Japan Spaceguard Association, 16.Kwansei Gakuin University, 17.JAMSTEC, 18.National Institute of Polar Research, 19.Kyoto University, 20.Saitama Prefectural University, 21.GITAI Japan, 22.Instituto de Astrofísica de Canarias, 23.University of Aizu, 24.Nagoya University, 25.Università d'Annunzio, 26.Arecibo Observatory & University of Central Florida, 27.JAXA)

Keywords:DESTINY+, Asteroid (3200) Phaethon, Geminid meteor shower, Cosmic dust, Flyby

DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science) is an upcoming flyby mission to Asteroid (3200) Phaethon. Phaethon is the parent body of Geminid meteor shower and an active asteroid, recurrently ejecting dust during the perihelion passage at 0.14 au. It will be launched in 2024 by a solid-fuel Epsilon S launch vehicle with kicking stage motors and flyby to Phaethon in January, 2028. DESTINY+ is a joint mission of technology demonstration and science observation. For the science observation, high-speed (36 km/s) flyby imaging of Phaethon at the closest distance of 500±50 km is conducted with a tracking telescopic camera (TCAP) and a VIS-NIR multiband camera (MCAP) with four bands (425, 550, 700, and 850 nm). Direct measurement of dynamical and chemical properties of each dust particle is performed in the entire mission phase, including the Earth spiraling-out phase, the lunar swing-by phase, the interplanetary cruising phase and Phaethon flyby phase, using a dust analyzer (DDA). DDA is an impact-ionization dust detector and time-of-flight mass spectrometer, equipped with a two-axis gimbal. The Preliminary Design Review (PDR) was complete in December, 2022. Functional tests and ground calibration activities using engineering models (EM) are currently underway for science instruments. Preliminary measurement of dust impact ionization TOF mass spectra with the DDA EM and the electrostatic accelerator installed at University of Stuttgart was successful.
Imaging of Phaethon will be conducted autonomously during the high-speed flyby. Detailed understanding of its characteristics, especially the size, shape, albedo, and rotation state prior to the flyby is crucial for successful imaging. In spite of the extensive ground-based observations of Phaethon during the close encounter in December, 2017 and observation campaigns for stellar occultation by Phaethon in 2019, there remain moderate uncertainty for the albedo, size and absolute magnitude. To better determine the albedo and size, polarimetric observation [1], photometric observation [2], and stellar occultation observation [3] with small solar phase angles were conducted in 2021 and 2022. Polarimetric observations were performed at Higashi-Hiroshima Observatory and Nishi-Harima Astronomical Observatory. The derived geometric albedo is Pv = 0.08–0.13 [1]. Photometric observations in the optical wavelength were performed with the TriCCS camera on the Seimei 3.8m telescope at the lower phase angles down to about 9 deg. The derived absolute magnitude Hv= 14.23 ± 0.02 [2]. With the above Hv value and the geometric albedo of Phaethon derived in the above polarimetric study [1], the Phaethon’s diameter is estimated to be within a range of 5.22 to 6.74 km, which is consistent with radar and occultation observations [2]. A stellar occultation by Phaethon, which occurred in western Japan and South Korea on 2021 October 3 (UTC) was conducted with a total of 72 observers at 36 stations [3]. Observational reductions show that the apparent cross-section of Phaethon at the time of the occultation could be approximated using an ellipse with a major diameter of 6.12 ± 0.07 km and a minor diameter of 4.14 ± 0.07 km, and a position angle of 117.4 ± 1.5 deg [3]. Another stellar occultation by Phaethon was observed in Hokkaido, Japan on 2022 October 21 (UTC) with a total of 36 observers at 19 stations. The latest shape model generated with a combination of the Arecibo radar data, multiple light curves from 1989 through 2022 and the stellar occultation results shows that the maximum extent along each axis is 6.4 × 6.1× 5.1 km and volume-equivalent diameter is 5.2 km [4].
[1] Geem, Ishiguro et al. (2022) MNRAS doi.org/10.1093/mnrasl/slac072.
[2] Beniyama, Sekiguchi et al. (2023) PASJ, doi.org/10.1093/pasj/psac109.
[3] Yoshida et al (2022) PASJ, doi.org/10.1093/pasj/psac096.
[4] Marshall et al (2022) DPS meeting #54, id. 514.07.