[P-PS03] 太陽系小天体：太陽系の形成と進化における最新成果と今後の展望

[PPS03-13] DESTINY+プロジェクトとサイエンスの最新状況

*荒井 朋子¹、小林 正規¹、石橋 高¹、吉田 二美²、木村 宏¹、平井 隆之¹、洪 鵬¹、岡本 尚也¹、和田 浩二¹、千秋 博紀¹、山田 学¹、秋田谷 洋¹、スラマ ラルフ³、クルーガ ハラルド⁴、石黒 正晃⁵、中村 智樹⁶、佐々木 晶⁷、薮田 ひかる⁸、渡部 潤一⁹、伊藤 孝士⁹、大坪 貴文⁹、大塚 勝仁¹⁰、紅山 仁¹¹、諸田 智克¹¹、三河内 岳¹¹、橘 省吾¹¹、廣井 孝弘¹²、関口 朋彦¹³、阿部 新助¹⁴、浦川 聖太郎¹⁵、松浦 周二¹⁶、伊藤 元雄¹⁷、山口 亮¹⁸、野口 高明¹⁹、小松 睦美²⁰、中村メッセンジャー 圭子²¹、巽 瑛理²²、平田 成²³、出村 裕英²³、小松 吾郎²⁵、金田 英宏²⁴、マーシャル ショーン²⁶、矢野 創²⁷、吉川 真²⁷、尾崎 直哉²⁷、山本 高行²⁷、豊田 裕之²⁷、西山 和孝²⁷、今村 裕志²⁷、高島 建²⁷ (1.千葉工業大学惑星探査研究センター、2.産業医科大学、3.シュツットガルト大学、4.マックスプランク研究所、5.ソウル大学、6.東北大学、7.大阪大学、8.広島大学、9.国立天文台、10.東京流星観測網、11.東京大学、12.ブラウン大学、13.北海道教育大学、14.日本大学、15.日本スペースガード協会、16.関西学院大学、17.海洋研究開発機構、18.国立極地研究所、19.京都大学、20.埼玉県立大学、21.ギタイ・ジャパン、22.カナリア天文物理学研究所、23.会津大学、24.名古屋大学、25.ダヌンツィオ大学、26.アレシボ天文台、27.宇宙研究開発機構)

キーワード：デスティニープラス、小惑星フェートン、ふたご座流星群、宇宙塵、フライバイ

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.