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

[PPS03-12] Current Status of DESTINY⁺ project and science

*Tomoko Arai¹, Masanori Kobayashi¹, Ko Ishibashi¹, Hiroshi Kimura¹, Takayuki Hirai¹, Takaya Okamoto¹, Manabu Yamada¹, Hiroshi Akitaya¹, Hiroki Senshu¹, Koji Wada¹, Fumi Yoshida^2,1, Ralf Srama³, Harald Krüger⁴, Tomokatsu Morota⁵, Sho Saski⁶, Hikaru Yabuta⁷, Tomoki Nakamura⁸, Katsuhito Ohtsuka^9,1, Masateru Ishiguro¹⁰, Tomohiko Sekiguchi¹¹, Seitaro Urakawa¹², Junnichi Watanabe¹³, Takashi Ito¹³, Takafumi Ootsubo², Shinsuke Abe¹⁴, Takahiro Hiroi¹⁵, Sean Marshall¹⁶, Goro Komatsu^17,1, Keiko Nakamura-Messenger¹⁸, Mutsumi Komatsu¹⁹, Jin Beniyama⁵, Shogo Tachibana⁵, Takashi Mikouchi⁵, Takaaki Noguchi²⁰, Hidehiro Kaneda²¹, Hirohide Demura²², Naru Hirata²², Motoo Ito²³, Akira Yamaguchi²⁴, Shuji Matsuura²⁵, Eri Tatsumi²⁶, Yasuhiro Yokota²⁶, Hajime Yano²⁶, Makoto Yoshikawa²⁶, Naoya Ozaki²⁶, Takayuki Yamamoto²⁶, Hiroyuki Toyoda²⁶, Kazutaka Nishiyama²⁶, Hiroshi Imamura²⁶, Takeshi Takashima²⁶ (1.Chiba Institute of Technology, 2.University of Occupational and Environmental Health, 3.University of Stuttgart, 4.Max Planck Institute, 5.The University of Tokyo, 6.Osaka University, 7.Hiroshima University, 8.Tohoku University, 9.Tokyo Meteor Network, 10.Seoul National University, 11.Hokkaido University of Education , 12.Japan Spaceguard Association, 13.National Astronomical Observatory of Japan, 14.Nihon University, 15.Brown University, 16.University of Central Florida, 17.D'Annunzio University, 18.Exploration Laboratories, 19.Saitama Prefectural University, 20.Kyoto University, 21.Nagoya University, 22.Aizu University, 23.JAMSTEC, 24.National Institute of Polar Research, 25.Kwansei Gakuin University, 26.JAXA)

Keywords:DESTINY+, Phaethon, Flyby, Cosmic dust, Geminid meteor shower, Active asteroids

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 was previously planned to be launched in FY 2024 by a solid-fuel Epsilon S rocket and flyby to Phaethon in January, 2028 [8], but the launch is now scheduled in FY 2025. 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, with 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 2022 and currently in the critical design phase for the spacecraft bus system and science payloads. 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 are on-going.
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. After 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. Continuing efforts of ground-based observation, including polarimetric observation [1], photometric observation [2], and stellar occultation observation [3] succeeded in better determining the albedo and size of Phaethon. The latest geometric albedo is Pv = 0.08–0.13 [1] and the absolute magnitude Hv= 14.23 ± 0.02 [2]. The latest shape model generated with a combination of the Arecibo radar data, multiple light curves from 1989 through 2022 and the stellar occultation observation outcomes in 2021 and 2022 in Japan 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]. Another observation campaign is planned for stellar occultation by Phaethon in the western part of Japan on November 16 this year.
For operational planning upon the closest flyby of Phaethon, we plan to observe km-scale large concavities near the equator and low latitude regions identified by the Arecibo radar observation [5]. With the currently available rotation period (3.603957±0.000001 (hr)) [6,7], pole orientation [6, 7] and the updated 3D shape model of Phaethon [4], the flyby timing can be adjusted to be able to observe the targeted areas on the surface of Phaethon during the closest approach. The current observation targets are either the feature b (>1 km in size) on the southern hemisphere or the feature d (2 km in size) on the northern hemisphere [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 (2023) DESTINY+ Science Working Team meeting 2023 abstract.
[5] Taylor P. A. et al. (2019) PSS 167,1.
[6] Kim M. -J. et al. (2018) A&A 619, A123.
[7] Hanuš J. et al. (2018) A&A 620, L8.