Distribution and Characteristics of Martian Precipitating H-ENA
Energetic Neutral Atom(ENA)is generated by charge exchange between energetic ions and background neutrals.As Martian exosphere extends far above the bow shock,hydrogen ENA(H-ENA)produced by solar wind proton may enter the lower atmosphere directly,depositing mass and energy in the atmosphere.Based on the single-fluid multispecies MHD model and exosphere model,this paper cal-culates the spatial distribution of the precipitating H-ENA flux at the height of 200 km on Mars,evalu-ates the particle and energy deposition rate of the precipitating H-ENA under different solar wind condi-tions,analyzes their controlling factors.The results show that the solar wind H-ENA generated up-stream of the bow shock is less affected by the crustal fields,and shows a cosZ distribution.As a major mass and energy source,the precipitating solar wind H-ENAs account for 59%particle deposition and 81%energy deposition of the total precipitating ENAs.Magnetosheath H-ENA generated in the magne-tosheath is greatly affected by the crustal fields,and their precipitating flux decreases significantly above the strongest magnetic anomalies.The precipitating H-ENA flux is proportional to the upstream solar wind flux,and 2.1%～3.5%of upstream solar wind protons are estimated to be converted into the solar wind H-ENAs.
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