Observation of CO2^++ dication in the dayside Martian upper atmosphere  

作　　者：Hao Gu Jun Cui DanDan Niu LongKang Dai JianPing Huang XiaoShu Wu YongQiang Hao Yong Wei 

机构地区：[1]State Key Laboratory of Lunar and Planetary Sciences,Macao University of Science and Technology,Macao 999078,China [2]School of Atmospheric Sciences,Sun Yat-Sen University,Zhuhai Guangdong 519082,China [3]Key Laboratory of Lunar and Deep Space Exploration,Chinese Academy of Sciences,Beijing 100101,China [4]Chinese Academy of Sciences Center for Excellence in Comparative Planetology,Hefei 230026,China [5]School of Earth and Space Sciences,Beijing University,Beijing 100871,China [6]Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [7]School of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Earth and Planetary Physics》2020年第4期396-402,共7页地球与行星物理（英文版）

基　　金：supported by the B-type Strategic Priority Program No.XDB41000000;funded by the Chinese Academy of Sciences,and the pre-research projects on Civil Aerospace Technologies No.D020105 and D020103;funded by China's National Space Administration;the National Science Foundation of China through grants 41525015 and 41774186 to JC,41904154 to WXS,and 41525016 to YW.

摘　　要：Doubly charged positive ions(dications)are an important component of planetary ionospheres because of the large energy required for their formation.Observations of these ions are exceptionally difficult due to their low abundances;until now,only atomic dications have been detected.The Neutral Gas and Ion Mass Spectrometer(NGIMS)measurements made on board the recent Mars Atmosphere and Volatile Evolution mission provide the first opportunity for decisive detection of molecular dications,CO2^++in this case,in a planetary upper atmosphere.The NGIMS data reveal a dayside averaged CO2^++distribution declining steadily from 5.6 cm^−3 at 160 km to below 1 cm^−3 above 200 km.The dominant CO2^++production mechanisms are double photoionization of CO2 below 190 km and single photoionization of CO2^+at higher altitudes;CO2++destruction is dominated by natural dissociation,but reactions with atmospheric CO2 and O become important below 160 km.Simplified photochemical model calculations are carried out and reasonably reproduce the data at low altitudes within a factor of 2 but underestimate the data at high altitudes by a factor of 4.Finally,we report a much stronger solar control of the CO2^++density than of the CO2+density.

关 键 词：MAVEN Martian ionosphere DICATION 

分 类 号：P185.3[天文地球—天文学]