MESSENGER Observations of Reconnection in Mercury's Magnetotail Under Strong IMF Forcing

Abstract

AbstractThe MESSENGER spacecraft typically crossed Mercury's magnetotail current sheet relatively close to the planet, that is, less than 2.5 RM (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 RM. In contrast, the dawnside events occur at altitudes of ∼1 RM. 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.