A MAVEN investigation of O++ in the dayside Martian ionosphere  

作　　者：Hao Gu Jun Cui ZhaoGuo He JiaHao Zhong 

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]Chinese Academy of Sciences Center for Excellence in Comparative Planetology,Hefei 230000,China [4]National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China

出　　处：《Earth and Planetary Physics》2020年第1期11-16,共6页地球与行星物理（英文版）

基　　金：support from the National Natural Science Foundation of China (NSFC) through grants 41525015, 41774186, 41704160, and 41804150

摘　　要：O^++ is an interesting species in the ionospheres of both the Earth and Venus. Recent measurements made by the Neutral Gas and Ion Mass Spectrometer (NGIMS) on board the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft provide the first firm detection of O^++ in the Martian ionosphere. This study is devoted to an evaluation of the dominant O^++ production and destruction channels in the dayside Martian ionosphere, by virtue of NGIMS data accumulated over a large number of MAVEN orbits. Our analysis reveals the dominant production channels to be double photoionization of O at low altitudes and photoionization of O^+ at high altitudes, respectively, in response to the varying degree of O ionization. O^++ destruction is shown to occur mainly via charge exchange with CO2 at low altitudes and with O at high altitudes. In the dayside median sense, an exact balance between O^++ production and destruction is suggested by the data below 200 km. The apparent discrepancy from local photochemical equilibrium at higher altitudes is interpreted as a signature of strong O^++ escape on Mars, characterized by an escape rate of 6×10^22s^-1.O++ is an interesting species in the ionospheres of both the Earth and Venus. Recent measurements made by the Neutral Gas and Ion Mass Spectrometer（NGIMS） on board the Mars Atmosphere and Volatile Evolution（MAVEN） spacecraft provide the first firm detection of O++ in the Martian ionosphere. This study is devoted to an evaluation of the dominant O++ production and destruction channels in the dayside Martian ionosphere, by virtue of NGIMS data accumulated over a large number of MAVEN orbits. Our analysis reveals the dominant production channels to be double photoionization of O at low altitudes and photoionization of O+ at high altitudes,respectively, in response to the varying degree of O ionization. O++ destruction is shown to occur mainly via charge exchange with CO2 at low altitudes and with O at high altitudes. In the dayside median sense, an exact balance between O++ production and destruction is suggested by the data below 200 km. The apparent discrepancy from local photochemical equilibrium at higher altitudes is interpreted as a signature of strong O++ escape on Mars, characterized by an escape rate of 6×1022 s–1.

关 键 词：MARS IONOSPHERE doubly ionized oxygen MAVEN 

分 类 号：P185.3[天文地球—天文学]