過去的地球案例顯示，當太陽風處於低阿爾文馬赫數（Alfvén Mach number）時，異常重聯層（Anomalous reconnection layer， ARL）會出現在磁鞘和磁層頂之間，由高緯度磁層頂的磁場重聯產生。ARL的結構類似於磁重聯外流區，即總磁場強度降低且高能離子流量增加的地方。因為地球周遭的太陽風環境大多處於高阿爾文馬赫數，很少觀測到這種事件，所以被稱作異常重聯層。根據過去的文獻記載，水星周遭的太陽風環境通常處於低阿爾文馬赫數，由此可以推測在水星磁層頂附近可以經常觀察到類似ARL的現象。為了驗證這個推測，我們調查了MESSENGER（MErcurySurface， SpaceENvironment， GEochemistry， and Ranging）太空船在水星磁鞘所獲得的磁場和離子通量資料，並找出116個重聯層穿越事件；這些事件是從MESSENGER資料中挑選出來的，其數量遠多於地球上發現的ARL事件，因此證實了類似ARL的重聯層結構經常在水星磁層環境出現的推測。同時也探討了水星重聯層的厚度大小，結果顯示重聯層的平均厚度是0.1單位的平均水星磁鞘厚度。本研究也比較了水星重聯層與極尖區的特徵，雖然部分重聯層與極尖區的緯度相似，但兩者之間存在明顯差異，即使在高緯度，兩者在磁場特性與觀測高度上不同。此外，極尖區在高能量的質子通量較重聯層高，而ARL在中等能量的質子通量則較高，說明兩者的粒子加速機制並不相同。此研究有助於更深入理解水星與地球磁層環境的差異，特別是在水星磁場重聯層的發生模式、特性與觀測結果方面。;A previous event found at Earth has shown that an Anomalous Reconnection Layer (ARL) forms in the magnetosheath near the magnetopause when the solar wind has a low Alfvén Mach number. Its structure， which is similar to a magnetic reconnection outflow region， is characterized by a weaker total magnetic field and a higher flux of high-energy ions than those outside the ARL region. Because the property of the solar wind around Earth is mostly at a high Alfvén Mach number， this kind of the event is rarely observed. Based on the past literature， the solar wind around Mercury is typically in a low Alfvén Mach number regime. Therefore， we can hypothesize that the ARL-like structure should be a common feature on Mercury′s magnetosphere. To test this， we identified 116 ARL-like crossing events using the magnetic field and ion flux data from the MESSENGER satellite. This large number supports our hypothesis that the ARL-like structure frequently occurs in Mercury′s magnetosphere. We also find that the average thickness of the layers is about one tenth of the magnetosheath′s thickness. This study also compared the characteristics of Mercury′s reconnection layer and the cusp region. Although some reconnection layers occur at latitudes similar to the cusp， significant differences remain; the two regions differ in magnetic field properties and observation altitudes even at high latitudes. Additionally， the cusp exhibits higher proton fluxes at high energies， whereas the ARL shows higher fluxes at intermediate energies， indicating that their particle acceleration mechanisms are difference. The present work helps deepen our understanding of the structural differences between the magnetospheres around Mercury and Earth.
