Mercury exosphere

In this paper, the potassium exosphere is modeled using laboratory measurements to constrain the various ejection processes. The annual cycle of the exospheric potassium emission brightness is compared to the few available observations showing that our model provides a reasonable description of this exospheric component. A comparison with the best spatially resolved observation of Doressoundiram et al. (Doressoundiram, A., Leblanc, F., Foellmi, C., Cremonese, G., Donati, F., Veillet, C. [2010]. Icarus 207, 1-8) highlights key features of the Na/K spatial distributions. It is essentially differences in global transport, the loss rate and the desorption efficiencies which account for the spatial distribution of the observed ratio. The Na/K ratio in the exosphere cannot be simply associated with the primary abundances but is closely related to the relative loss rates. Accounting for the transport and loss, the observed Na/K exospheric ratio may be consistent with an initial abundance close to solar or meteoritic ones.