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ISSN  2096-3955

CN  10-1502/P

Citation: Gu, H., Cui, J., Niu, D. D., Dai, L. K., Huang, J. P., Wu, X. S., Hao, Y. Q., and Wei, Y. (2020). Observation of CO2++ dication in the dayside Martian upper atmosphere. Earth Planet. Phys., 4(4), 1–7doi: 10.26464/epp2020036

doi: 10.26464/epp2020036


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


State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, China


School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai Guangdong 519082, China


Key Laboratory of Lunar and Deep Space Exploration, Chinese Academy of Sciences, Beijing 100101, China


Chinese Academy of Sciences Center for Excellence in Comparative Planetology, Hefei 230026, China


School of Earth and Space Sciences, Beijing University, Beijing 100871, China


Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China


School of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

Corresponding author: Jun Cui,

Received Date: 2020-03-28
Web Publishing Date: 2020-07-01

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 .

Key words: MAVEN; Martian ionosphere; dication

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

Hao Gu, Jun Cui, DanDan Niu, LongKang Dai, JianPing Huang, XiaoShu Wu, YongQiang Hao, Yong Wei