Electron‐Only Tail Current Sheets and Their Temporal Evolution.

The Earth's magnetotail contains a current sheet separating the anti‐Sunward field of the southern lobe from the sunward‐pointing northern lobe. Herein, we report tail current sheets that are supported only by electron currents. We examine one electron‐only current sheet in detail and briefly discuss 10 others. Three current sheets are interpreted in terms of the time‐evolution of reconnection onset. These current sheets show evidence of parallel electron heating, perpendicular ion heating, and current sheet expansion. These features are consistent with electron and ion behavior during traditional "electron‐ion" reconnection. Ground‐based and in‐situ data show that electron‐ion reconnection occurs shortly after each "pre‐ion reconnection" electron‐only reconnection event. This suggests that electron‐only reconnection can act as a precursor to electron‐ion reconnection. We note that five events occur shortly after a period of electron‐ion reconnection, which suggests that electron‐only reconnection is more than merely a precursor to ion reconnection. Plain Language Summary: Magnetic reconnection is a key process in conversion of magnetic energy to kinetic and thermal energy in space and laboratory plasmas. The Magnetosphere Multiscale (MMS) mission is designed to study the physics of magnetic reconnection with unparalleled time and spatial resolution. In this letter, we present several MMS observations of electron‐supported current sheets that do not show signatures of typical magnetic reconnection, dubbed "Electron‐Only" reconnection. We use three events to show that "electron‐only" reconnection can lead to "electron‐ion" magnetic reconnection. We use six events to suggest that "electron‐only" reconnection occurs in more regimes than merely during the onset of "electron‐ion" reconnection. Key Points: Eleven electron‐only reconnection events observed by Magnetosphere Multiscale in the near‐Earth magnetotailThree events are snapshots in a time evolution into "electron‐ion" reconnectionFive events occur after "electron‐ion" reconnection; Electron‐only reconnection is more than a precursor to "electron‐ion" reconnection [ABSTRACT FROM AUTHOR]