MESSENGER Observations of Reconnection in Mercury’s Near‐Magnetotail Under Strong IMF Forcing

The MESSENGER spacecraft typically crossed Mercury's magnetotail current sheet relatively close to the planet, that is, less than 2.5 R-M (planet radius; 2,440 km). Magnetometer measurements are used to detect active reconnection events by identifying the quadrupole Hall magnetic field signatures that form about X-lines. Statistical analyses of the 51 active reconnection events detected in this manner indicate that they occur most frequently on the duskside and typically at a mean altitude greater than 1.5 R-M. In contrast, the dawnside events occur at altitudes of & SIM;1 R-M. In addition, a higher recurrence rate of flux ropes formed in the Hall region was observed on the dawnside. Applying the Kan-Lee solar wind-magnetosphere coupling function confirmed that these near-tail reconnection events at Mercury are observed under strong forcing by the interplanetary magnetic field. We further propose that the reconnection-driven nightside magnetosphere-planet interaction is characterized by a pronounced dawn-dusk asymmetry and may significantly influence the near-Mercury space environment.