水星磁尾磁场重联的卫星观测研究

Magnetic reconnection is a key mechanism of driving magnetospheric dynamics. Comparing magnetic reconnection in different planetary space environment will help to understanding the nature of magnetosphere dynamics. Mercury’s comparatively weak intrinsic magnetic field, together with the strong solar wind forcing in the inner heliosphere, creates a small and highly dynamic magnetosphere. In situ observations of magnetotail magnetic reconnection is a key to understanding the Mercury’s highly dynamics. However, no direct onsite detection of reconnection sites at Mercury has been made. This project will use the MESSENGER spacecraft to cross the magnetotail current sheet data from 2011 to 2015 to find the magnetic reconnection events and establish a library of cases. Based on the typical events research and statistical analysis, we plan to get the common signatures of magnetic reconnection in Mercury’s space environment with weak intrinsic magnetic field, to reveal the nature of magnetic reconnection occurrence in the magnetosphere, to connect the relation of magnetotail reconnection with the distribution of energetic electrons in the magnetosphere, to evaluate the characteristic and efficiency of magnetic flux transportation to inner magnetosphere through tail reconnection. Comparing with Earth, this project will achieve the breakthroughs and innovative progresses in the understanding of the Mercury’s magnetospheric dynamics such as the time scales, the spatial characteristics, and the origin of the magnetospheric energetic particles. This project will be the first observations of magnetic reconnection in Mercury’s space, and will obtain the different signatures of magnetic reconnection to the Earth.

磁场重联是驱动行星磁层动力学过程的重要机制。研究不同行星空间环境下的磁场重联有助于我们梳理行星磁层的变化规律。水星轨道处强太阳风驱动和弱行星磁场相互作用形成太阳系中尺度最小、动力学特征最活跃的行星磁层。观测研究磁尾重联是理解水星磁层动力学急剧过程的关键。但是，至今仍未见有关水星磁重联的观测报导。本项目利用“信使”号卫星2011-2015年穿越磁尾电流片数据，筛选磁重联事件，建立事例库；通过典型事例研究并结合统计分析，获得磁场重联在水星弱磁层空间环境下的一般特征；揭示磁重联在磁尾空间发生的规律；建立磁尾重联与磁层高能电子分布的联系；评估通过磁尾重联向内磁层传输磁通的特征与效率。对比地球，以期在水星磁层大尺度动力学过程的时间尺度、空间特征、磁层高能粒子的起源等磁层动力学过程的理解上取得重点突破和创新性进展。本项目将首次对水星空间磁场重联进行直接观测，有望获得不同于地球空间磁场重联的一般性特征。

观测研究水星磁尾磁重联是理解水星磁层动力学急剧过程的关键，也有助于梳理行星磁层的变化规律。本项目主要研究磁重联在水星空间环境中的一般表现特征及在磁尾空间发生的规律。取得了以下研究结果：（1）建立了完整的“信使”号卫星穿越水星磁尾电流片及对应的磁重联事件库；（2）发现了水星空间超大磁通量绳的存在证据并提出了相应的形成机制；（3）提出了水星磁通量传输事件形成机理；（4）发现了强行星际磁场驱动下水星磁尾磁重联空间分布特征，并提出水星夜侧磁层与星体相互作用的晨昏不对称性。研究结果给出了水星磁层动力学过程的新物理图像，加深了对太阳风与行星磁场相互作用过程的理解。