Earth's magnetic field creates a protective bubble known as the magnetosphere, which surrounds the planet and shields us from solar wind. The moon's electric charge was discovered by the Kayuga (Selene) lunar orbiter, managed by the Japan Aerospace Exploration Agency (JAXA). Scientists are now mining the data sent back by the craft's imagers and instruments, which recorded that relatively high-energy electrons are being absorbed by the lunar surface when the moon is full.
The result is an electrostatic charge building up in the first few meters above the lunar surface once a month, creating a temporary electric field. Based on Kaguya's data, the team says this lunar electrification happens when the moon passes through the region of the magnetosphere called the plasma sheet, which runs down the middle of Earth's magnetotail. Since the moon has no global magnetic field of its own, its surface remains exposed to the trapped solar particles that are gyrating inside the plasma sheet.