Inside a Lunar Mini-Magnetosphere: First Energetic Neutral Atom Measurements on the Lunar Surface

Due to lack of in situ observations, people still know little about the formation conditions and the internal structure of lunar mini-magnetosphere. Here we present the first energetic neutral atom (ENA) measurement on lunar surface by the Chang'E-4 mission. It is found that when downstream from the Imbrium antipode magnetic anomalies, the measured ENA fluxes are generally decreased, suggesting a mini-magnetosphere that can shield the lunar surface from the solar wind. Further studies show that the shielding effect can only be found when the ion inertia length is small (<120 km) and some solar wind ions can penetrate into the mini-magnetosphere with a penetrating efficiency positively correlated with the solar wind dynamic pressure. When the ion inertia length is large, no shielding effect can be found. With the help of Hall MHD simulations, we confirm the existence of a mini-magnetosphere and the shielding effect anti-correlated with ion inertia length.

Automated summary

The first energetic neutral atom (ENA) measurement on the lunar surface by the Chang'E-4 mission revealed the potential existence of a mini-magnetosphere that can shield the lunar surface from solar wind under certain conditions. The shielding effect is correlated with the ion inertia length and can prevent solar wind ions from penetrating into the mini-magnetosphere. The existence of the mini-magnetosphere and its shielding effect were confirmed through Hall MHD simulations.