Intermittent Electron-Only Reconnection at Lunar Mini-Magnetospheres

Lunar crustal magnetic anomalies (LCMA) are sub-ion-gyroradius structures that have been shown to stand off the solar wind (SW) plasma from the Moon's surface, forming shock-like discontinuities and reflecting incident SW protons. In this letter, the results of high-resolution, two-dimensional fully kinetic simulations show a bursty electron-only magnetic reconnection in the SW-LCMA interaction region, characterized by the quasi-periodic formation and ejection of magnetic islands and strong parallel electron flows along the X-point separator lines. The islands are observed to modify the magnetic pressure pile-up and Hall electric field above the LCMA, leading to sharp increases in reflected protons that drive electromagnetic fluctuations downstream and short distances upstream in the SW.