日本地球惑星科学連合2014年大会

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セッション記号 P (宇宙惑星科学) » P-PS 惑星科学

[P-PS23_2PM1] 月の科学と探査

2014年5月2日(金) 14:15 〜 16:15 413 (4F)

コンビーナ:*諸田 智克(名古屋大学大学院環境学研究科)、本田 親寿(会津大学)、西野 真木(名古屋大学太陽地球環境研究所)、長岡 央(早稲田大学先進理工学部)、座長:Nishino Masaki N(Solar-Terrestrial Environment Laboratory, Nagoya University)、石山 謙(東北大学大学院理学研究科地球物理学専攻)

15:00 〜 15:15

[PPS23-18] 月のアルカリ外気圏の構造と変動

*横田 勝一郎1斎藤 義文1浅村 和史1Nishino Masaki N2綱川 秀夫3 (1.宇宙研、2.名大太陽地球環境研究所、3.東工大)

キーワード:月, 外気圏, アルカリ大気, 質量分析

Lunar exosphere has been observed and studied on many occasions by ground-based telescopes since the discovery of surface-bounded alkali exosphere. The observed exospheric components were alkali atoms such as Na and K because the emission lines are much brighter than for other conceivable components. The structure, source, and the transport mechanisms of the lunar exosphere have been discussed based on these ground-based observations of the alkali atoms. As for the source mechanism of the thin lunar alkali exosphere, five processes were proposed as follows: thermal desorption, electron-stimulated desorption (ESD), photon-stimulated desorption (PSD), ion-induced desorption (sputtering), and vaporization by micrometeoroid impacts. Structure of the lunar exosphere gives us the key parameters to investigate the source mechanism. The observed Na exosphere distribution suggested that PSD and/or sputtering do not simply release the exospheric particles. Since PSD is capable of releasing alkali atoms only out of very shallow region in the lunar soils, PSD has relatively limited store of the exospheric particles in the lunar surface. If there was no replenishing process, PSD would deplete surface alkalis. We present latitude and longitude distributions of Na+ and K+ fluxes from the Moon derived from the Kaguya low-energy ion data. Although the latitude distribution agrees with the previous ground-based telescope observations, dawn-dusk asymmetry has been found in the longitude distribution. Our model of the lunar surface abundance and yield of Na and K demonstrates that the abundance decreases to around 50%, at dusk compared to that at dawn due to the emission of the exospheric particles. It is also implicated that the surface abundance of Na and K need to be supplied during the night in order to explain the observed lunar exosphere with the dawn-dusk asymmetry.