Mercury is the archetype of a weakly magnetized, airless, telluric body
immersed in the solar wind. Due to the lack of any substantial atmosphere, the
solar wind directly precipitates on Mercury's surface. Using a 3D fully-kinetic
self-consistent plasma model, we show for the first time that solar-wind
electron precipitation drives (i) efficient ionization of multiple species (H,
He, O and Mn) in Mercury's neutral exosphere and (ii) emission of X-rays from
the planet's surface. This is the first, independent evidence of X-ray auroras
on Mercury using a numerical approach.Comment: Submitted to Physical Review Letter