Acceleration of scattered solar wind protons at the polar terminator of the Moon: Results from Chang'E‐1/SWIDs

We report accelerated particles observed by Solar Wind Ion Detectors (SWIDs) on Chang'E‐1 spacecraft close to terminator regions of the Moon. As the spacecraft crosses the terminator, a stream of ions with energy of ∼200eV/q are detected. As the spacecraft moves to the anti‐subsolar point of the Moon, the energy of these ions increase by 600 ∼ 1500eV. This phenomenon occurs at north/south pole when IMF By component is dominant and negative/positive. It is proposed these particles are scattered solar wind protons, accelerated by the convection electric field of the solar wind and E × B drift in the ambipolar electric field at the flank of the lunar wake. This mechanism allows a new portion of solar wind protons to enter the central lunar wake, and provides a possibility to study the property of proton scattering at the dayside of the Moon.