火星弓激波上游高能拾起氧离子实例分析  

In situ observation of energetic pickup oxygen ions upstream from the Martian bow shock:a case study

作　　者：雷桓 郭建鹏[1,2] 何林峡 林海博 常克文 陈艳 LEI Huan;GUO JianPeng;HE LinXia;LIN HaiBo;CHANG KeWen;CHEN Yan(Institute for Frontiers in Astronomy and Astrophysics,Beijing Normal University,Beijing 102206,China;Planetary and Space Physics Group,Department of Astronomy,Beijing Normal University,Beijing 100875,China)

机构地区：[1]北京师范大学天文与天体物理前沿科学研究所,北京102206 [2]北京师范大学天文系行星与空间物理研究团组,北京100875

出　　处：《地球物理学报》2024年第1期12-20,共9页Chinese Journal of Geophysics

基　　金：“中国科学院战略性先导科技专项”(XDB 41000000);国家自然科学基金项目(42074212,42374214);民用航天技术预先研究项目(D020104);中国科学院地质与地球物理研究所重点项目(IGGCAS-201904)资助。

摘　　要：火星外逸层中的氧原子(O)经光致电离、电荷交换或电子碰撞产生氧离子(O^(+)),新生O^(+)随即被太阳风拾起,进而被对流电场加速.这些O^(+)被称为“拾起”O^(+).2018年11月17日08∶54∶00—10∶24∶00 UT期间,火星大气和挥发物演化任务(Mars Atmosphere and Volatile EvolutioN,MAVEN)卫星从上游太阳风进入磁鞘中,持续观测到背离太阳运动的高能拾起O^(+)(约30 keV),在相空间呈现为初速度不为零的部分环分布.分析表明:这部分高能O^(+)的初始能量较高,回旋半径较大,位于摆线运动的高能区域,穿越火星弓激波进入磁鞘,离子在该范围内能量变化不显著,只是使得相应环分布在穿越弓激波后发生偏转.这些结果有助于进一步认识火星空间高能拾起O^(+)的产生与运动轨迹.The O atoms in the Martian exosphere can be ionized by photoionization,charge exchange,or electron impact.The newborn O~+ions are immediately picked up by the solar wind electromagnetic fields,and are then accelerated by the convection electric field.They are called pickup O~+ions.During 08∶54∶00—10∶24∶00 UT on 2018 November 17,and Mars Atmosphere and Volatile EvolutioN(MAVEN)observed persistent pickup O~+population with energies of~30 keV.They correspond to precipitating O~+ions coming from the upstream solar wind.In phase space,they are located near the middle phase of partial ring distribution with an initial velocity(i.e.,near the maximum energy of the partial ring distribution).Our analysis suggests that these precipitating energetic O~+can overcome the electrostatic bow shock potential and proceed downstream.Then,they are subject to the enhanced magnetic field in the magnetosheath.The results will help better understand the generation and the motion trajectories of energetic O~+ions at Mars.

关 键 词：火星 拾起氧离子 MAVEN 

分 类 号：P353[天文地球—空间物理学]