Energetic neutral atom imaging of Mercury's magnetosphere 1. Distribution of neutral particles in an axially symmetrical exosphere

We have developed a simple analytical model to obtain density distributions of neutral particles in an axially symmetrical exosphere. Correction due to the finite lifetime of exosphere neutral particles has been introduced. The model developed will be utilised in the simulations of energetic neutral atom production via charge-exchange reaction in Mercury's magnetosphere. As examples, we have calculated density profiles of helium and oxygen in Mercury's exosphere. We have also calculated the day side distribution of sodium atoms to demonstrate the effect of the finite lifetime.