[P-PS04] 火星と火星衛星

[PPS04-01] Martian Moons eXploration MMX: An overview focusing its science.

*倉本 圭^1,2、川勝 康弘²、藤本 正樹²、Barucci Maria Antonietta³、玄田 英典⁴、平田 成⁵、今村 剛⁶、Helbert Jörn⁷、亀田 真吾^8,2、小林 正規⁹、草野 広樹¹⁰、Lawrence David J.¹¹、松本 晃治¹²、Michel Patrick¹³、宮本 英昭⁶、中川 広務¹⁴、中村 智樹¹⁴、小川 和律²、大嶽 久志²、尾崎 正伸²、Russell Sara¹⁵、佐々木 晶¹⁶、千秋 博紀⁹、寺田 直樹¹⁴、Ulamec Stephan⁷、臼井 寛裕²、和田 浩二⁹、横田 勝一郎¹⁶ (1.北海道大学、2.宇宙航空研究開発機構、3.パリ天文台、4.東京工業大学、5.会津大学、6.東京大学、7.DLR、8.立教大学、9.千葉工業大学、10.量子科学技術研究開発機構、11.ジョンズ・ホプキンス大学、12.国立天文台、13.コート・ダジュール大学、14.東北大学、15.自然史博物館、16.大阪大学)

キーワード：MMX、フォボス、ダイモス、火星大気、起源と進化

The MMX mission, which is under development by JAXA, is the world's first mission to make a round trip to the Martian system. The exploration target includes not only both Martian moons comparable to asteroids but also the Martian atmosphere and circum-Martian space. There are two leading hypotheses for the origin of the Martian moons: One is the capture of primitive carbonaceous asteroids as suggested by the reflectance spectra, and the other is the in-situ formation from a circum-Martian disk composed from ejecta generated by a giant impact onto proto-Mars inferred from the small orbital eccentricities and inclinations of both moons. Regardless of which theory is correct, the Martian moons are thought to contain information about the composition and source regions of small bodies accreted on Mars in the final stages of its formation, the processes delivering volatile materials to terrestrial planets possibly from the outer solar system, and the physicochemical state of early Mars. MMX will determine the origin of the Martian moons and decode the above records, which are important clues to understanding the formation processes of habitable planets. After the launch by an HIII rocket planned in 2024, the MMX spacecraft will reach the Martian sphere after a ~1-year cruise. During the ~3-year stay in the Martian system, MMX will observe the Martian moons and Mars including sampling from Phobos. Then it will leave the Martian system to return to Earth in 2029. The MMX spacecraft will land at two sites to collect materials with different spectral characteristics. Before the first landing, detailed observations of Phobos will be done to select landing sites that satisfy accessibility to fresh bedrock materials and safety of spacecraft landing. Using a telescopic camera (TENGOO), LIDAR, a visible multiband camera (OROCHI), and a near-infrared spectroscopic imager (MIRS), the topography and surface composition of Phobos will be revealed at high special resolution and coverage from quasi-satellite orbits around this moon. These observations, together with gamma-ray and neutron spectrometers (MEGANE) and a mass spectrum analyzer (MSA) will provide data on the composition of the Phobos which are crucial to constrain the origin of the Phobos independently of the sample analysis. A small rover will be deployed and make in-situ observations of Phobos surface, which will contribute to the understanding of the geologic context of the sampling site. The high spatial resolution data of the characteristic geological structures of Phobos will clarify the evolutionary process of the moons' surfaces. The dust detector (CMDM) will provide data that will contribute to the understanding of moons' resurfacing processes caused by impacts of micrometeorites, and will attempt to detect hypothesized dust rings along the orbit of Martian moons. Observations of Deimos will constrain the origin and geological evolution of this moon in comparison with Phobos. Observations of the Martian atmosphere will reveal the dynamics of the transport of dust and water vapor between surface reservoirs and into the upper atmosphere. MSA will be used to measure the escape flux of Martian atmospheric constituents to space to constrain the atmospheric evolution. The origin of Phobos will be firmly determined from the microstructure, mineral, chemical, and isotopic compositions of the returned sample: these data will also constrain the source region of the captured body or the moons-forming impactor. By combining the sample dating, we will reveal the timing of the capture or the giant impact, the formation and evolution of the small body before the capture, and the surface evolution over geologic history as a Martian moon. Ejected materials from young impact craters on Mars, which are likely to be mixed in Phobos samples with a small fraction, may provide us with unique constraints on the evolution and habitability of the Martian surface environment.