*益永 圭¹、関 華奈子¹、Brain David²、Fang Xiaohua²、Dong Yaxue²、Jakosky Bruce²、McFadden James³、Halekas Jasper⁴、Connerney Jack⁵ (1.東京大学大学院理学研究科地球惑星科学専攻、2.Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, USA、3.Space Science Laboratory, University of California Berkeley, USA、4.Department of Physics and Astronomy, University of Iowa, USA、5.NASA Goddard Space Flight Center, USA)