[P-PS05] 火星と火星衛星

[PPS05-P13] A technique of retrieving the exospheric number density distribution from pickup ion ring distributions observed by MAVEN/STATIC and its application to future MMX/MSA observations

*益永 圭¹、寺田 直樹²、Leblanc Francois³、堺 正太朗²、横田 勝一郎⁴、原田 裕己⁵、原 拓也⁶、関 華奈子⁷、山崎 敦¹、臼井 寛裕¹ (1.宇宙航空研究開発機構、2.東北大学大学院理学研究科地球物理学専攻、3.LATMOS, Sorbonne Universite、4.大阪大学大学院理学研究科、5.京都大学大学院理学研究科、6.カリフォルニア大学バークレー校、7.東京大学大学院地球惑星科学専攻)

キーワード：火星、ピックアップイオン、外気圏、MAVEN、MMX

Ion pickup by the solar wind is ubiquitous in space plasma, generating pickup ions. Because pickup ions are originally produced by ionization of the exospheric neutral atmosphere, their measurements contain information on the exospheric neutral abundance. Here we establish a method to retrieve exospheric number densities, by analyzing ion velocity distribution functions of pickup ions measured by the Mars Atmosphere and Volatile EvolutioN spacecraft. We retrieved exospheric oxygen density distribution between altitudes of ~1,000 km and 10,000 km around Mars. The consistency between the retrieved oxygen density distribution the modeled density distribution of the Exospheric General Model suggests that the oxygen atoms are mainly produced by dissociative recombination of O₂⁺ in the Martian ionosphere. This method may be applied to other space missions to study the upper atmosphere of planets, moons, and small bodies in the solar system, where pickup ions exist. In this presentation, we discuss the application of this method to our future observations of the Mass Spectrum Analyzer on the Martian Moons eXploration spacecraft.