Host: The Japanese Society for Planetary Sciences: Local Organizing Committee for 2006 Fall Meeting
We have investigated the local-time (LT) dependence of distribution of Mercury's sodium exosphere, in order to understand production and loss processes of low release velocity component of the exosphere. As a method of the investigation, we compare a model sodium exosphere simulated by the Monte Carlo method with observation results [Sprague et al.,1997]. As an initial step of this investigation, we adopted the photon-stimulated desorption process as the released mechanism, and assumed that amount of sodium atoms supplied to Mercury's surface always exceeds that of released atoms from surface. As the results of the comparison the model could not meet with the observed LT dependence. It is suggested that, therefore, some additional mechanisms or effects, especially balance of supply and release for sodium atoms, should be considered. Following these results, we have investigated the LT dependence further by adopting new models considering non-uniformity of sodium atoms supplied to Mercury's surface and thermal desorption which is one of release mechanisms causes increase of sodium column density particularly at the dawn side region [Sprague et al.,1992; Hunten and Sprague,2002].
