  The link between the surface temperature of Mercury and the exosphere sodium
content has been investigated. Observations show that, along the orbit of
Mercury, two maxima of total Na content are present: one at aphelion and one at
perihelion. Previous models, based on a simple thermal map, were not able to
reproduce the aphelion peak. Here we introduce a new thermophysical model
giving soil temperatures as an input for the IAPS exospheric model already used
in the past with the input of a simple thermal map. By comparing the reference
model output with the new one, we show that such improved surface temperature
map is crucial to explain the temporal variability of Sodium along the orbit.
