Sun and Moon do proton dance

European Space Agency

Data from an instrument on Chandrayaan-1, the Indian lunar orbiter, suggest that charged particles from the Sun are rebounding from the Moon as hydrogen. Protons stream in from the solar wind and collide with the lunar surface. Most protons are caught in the regolith (moon dust) but one in five bounces back into space, picking up an electron in its path to create a hydrogen atom.

No one guessed that the Moon is a hydrogen mirror, reflecting protons back into space as hydrogen. This paves the way for a new imaging technique that could capture hydrogen emission by other atmosphere-free objects, such as Mercury or asteroids.