Effects of the charge exchange of solar wind with the Martian exosphere

Charge exchange of solar wind with the Martian exosphere is shown to have two-fold consequences. From the solar wind perspective, the thermal pressure is removed by charge exchange with Martian neutral particles. To maintain a constant total pressure in the flow, increase of magnetic field occurs and therefore accounts for the formation of the magnetic pileup boundary observed by the Mars Global Surveyor Magnetometer. To simulate this a fluid model is constructed and results from it are shown to successfully fit observations. On the other hand, the Martian exosphere is affected by the charge exchange, too. Compared to Venus, Mars has an ionosphere that is so dilute that charge exchange of solar wind should play an important role in the formation of a nonthermal Martian hydrogen exosphere component. In order to study quantitatively how the Martian exosphere is influenced by it, we develop a 3-dimensional Monte Carlo exosphere model in which effects of charge exchange with solar wind are isolated. Simulation results show the existence of that hot population does change the exospheric temperature structure greatly, and we also investigate the simulation results by calculating the contribution of the hot component to Ly-alpha emission and comparing it with data acquired by Mariners' ultraviolet spectrometers. Finally, it is concluded that charge exchange is important in the interaction between solar wind and Martian exosphere. Output of our models can be used in future modeling and data analysis for the coming Mars missions