Photoemission on the surface of Mercury and related electrical phenomena

Solar photons interact with the surface of Mercury due to the absence of an atmosphere. Photo-electrons are emitted from the sunlit hemisphere with a mean kinetic energy of about 1.6 eV. The current density lies in the range 0.1-0.2 mAm−2 at the subsolar point and is maximum at perihelion. Photoemission provides the means of a direct electrical coupling between the planet and its magnetospheric environment and sets a lower limit of the order of 10−5 S to the conductance of the surface of a derfectly insulating regolith.