Emission of negative ions, positive ions and energetic neutral atoms from the lunar surface caused by solar wind precipitation

A sizeable fraction of solar wind protons precipitating onto the lunar surface is backscattered from the lunar surface. Additionally the lunar surface is sputtered by the precipitating particle populations. Previous observations by spacecraft from orbit (Chandrayaan-1, Kaguya, IBEX) and from the lunar surface (Chang'e-4) show that up to 20% of the impinging solar wind protons are backscattered as energetic neutral atoms and about 0.1% to 1%  are backscattered as protons. However, particles emitted from the surface can have any charge state. The recent discovery of negative ions by the Negative Ions at the Lunar Surface (NILS) instrument on Chang'e-6 allows for the first time to investigate the full charge state distribution of solar wind induced backscattered and sputtered particle populations from the lunar surface. We present and interpret new data obtained from the lunar surface and discuss the impact of the emitted particle populations on the lunar exo-ionosphere.