A Comparison of the Importance of Electron-Stimulated Desorption of Sodium at Mercury and the Moon

We revisit the importance of Electron-Stimulated Desorption (ESD) as a source of neutral Na atoms and Na⁺ ions in the exospheres of Mercury and the Moon. For the first time we have calibrated the ESD yield per electron as a function of electron energy in the energy range 100 - 950 eV. This calibrated yield per electron was convolved with the electron flux as a function of energy onto Mercury's cusps to determine the average release rate of Na⁺ to the exosphere, using electron flux and cusp area estimates from a recent hybrid magnetosphere model (Lavorenti et al., 2023). Given that previous work showed the ESD yields of ions and neutral atoms are approximately equal, we compared the energy-weighted ESD release rate of Na⁺ to that derived from impact vaporization, photon-stimulated desorption, and ion-sputtering. We conclude that ESD is not a significant source of neutral Na atoms or Na⁺ ions to Mercury's exosphere. The electron flux and open regions are quite different at the Moon. The lunar surface is open to the solar wind since the Moon does not have a global magnetic field. The electron flux onto the Moon is taken from Artemis data.