Magnetospheric Multiscale (MMS), a NASA four-spacecraft constellation mission launched on March 12, 2015, will investigate magnetic reconnection in the boundary regions of the Earth’s magnetosphere, particularly along its dayside boundary with the solar wind and the neutral sheet in the magnetic tail. The most important goal of MMS is to conduct a definitive experiment to determine what causes magnetic field lines to reconnect in a collisionless plasma. The significance of the MMS results will extend far beyond the Earth’s magnetosphere because reconnection is known to occur in interplanetary space and in the solar corona where it is responsible for solar flares and the disconnection events known as coronal mass ejections. Active research is also being conducted on reconnection in the laboratory and specifically in magnetic-confinement fusion devices in which it is a limiting factor in achieving and maintaining electron temperatures high enough to initiate fusion. Finally, reconnection is proposed as the cause of numerous phenomena throughout the universe such as comet-tail disconnection events, magnetar flares, supernova ejections, and dynamics of neutron-star accretion disks. The MMS mission design is focused on answering specific questions about reconnection at the Earth’s magnetosphere. The prime focus of the mission is on determining the kinetic processes occurring in the electron diffusion region that are responsible for reconnection and that determine how it is initiated; but the mission will also place that physics into the context of the broad spectrum of physical processes associated with reconnection. Connections to other disciplines such as solar physics, astrophysics, and laboratory plasma physics are expected to be made through theory and modeling as informed by the MMS results.

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磁层多尺度概述和科学目标

磁层多尺度 (MMS) 是 NASA 于 2015 年 3 月 12 日发射的四航天器星座任务，将研究地球磁层边界区域的磁重联，特别是沿其与太阳风的日侧边界和磁尾中的中性层. MMS 最重要的目标是进行明确的实验，以确定导致磁场线在无碰撞等离子体中重新连接的原因。MMS 结果的重要性将远远超出地球磁层，因为已知重联发生在行星际空间和日冕中，在那里它对太阳耀斑和称为日冕物质抛射的断开事件负责。实验室中也正在积极研究重新连接，特别是在磁约束聚变装置中，在这些装置中，它是实现和保持足够高以引发聚变的电子温度的限制因素。最后，重新连接被认为是整个宇宙中许多现象的原因，例如彗尾断开事件、磁星耀斑、超新星抛射和中子星吸积盘的动力学。MMS 任务设计的重点是回答有关地球磁层重新连接的具体问题。任务的主要重点是确定发生在电子扩散区的动力学过程，这些过程负责重新连接并决定它是如何启动的；但该任务还将将该物理学置于与重新连接相关的广泛物理过程的背景下。预计将通过基于 MMS 结果的理论和建模与其他学科（如太阳物理学、天体物理学和实验室等离子体物理学）建立联系。