Direct Detection of Ongoing Magnetic Reconnection at Mercury's High-Latitude Magnetopause

An ongoing magnetic reconnection event was detected in the Mercury's high latitude magnetopause during a northward interplanetary magnetic field. The reconnection X-line region was revealed in the Mercury's magnetopause based on the encountered flux ropes ejected away from this region both planetward and tailward. A series of magnetic flux ropes, known as flux transfer event shower were observed tailward of this X-line region. These flux ropes were probably expanding and deflected as they were ejected away tailward from the X-line region. Large-amplitude variations in all three components of the magnetic field and a few small-scale flux ropes were observed inside the X-line region, which could be the seed of the flux rope shower at the magnetopause. The observations suggest that magnetic reconnection is highly dynamic and persistent in Mercury's magnetosphere. Magnetic reconnection has been regarded as the most important process for dynamics of the Mercury's magnetosphere and for the interaction between the solar wind and the Mercury's magnetosphere also. Although magnetic flux ropes and flux transfer events (FTEs) resulting from magnetic reconnection have been extensively observed in the Mercury's magnetosphere, the key region of magnetic reconnection, namely the X-line region, has never been reported so far by the spacecraft. Here, we present the first evidence of the reconnection X-line region in the Mercury's magnetosphere. A few small-scale magnetic flux ropes are observed inside the reconnection X-line region, which could be the seed of the observed magnetic FTE shower. Furthermore, the evolution of these flux ropes is addressed also based on the spacecraft observations. A reconnection X-line region is first observed in the Mercury's magnetopause during the northward interplanetary magnetic field The small-scale magnetic flux ropes in the X-line region could be the seed of the flux transfer event shower The flux ropes probably expand and is deflected after they are ejected away from the X-line region