Observations of Extreme ICME Ram Pressure Compressing Mercury’s Dayside Magnetosphere to the Surface
Observations of Extreme ICME Ram Pressure Compressing Mercury’s Dayside Magnetosphere to the Surface
复制标题
极端 ICME 冲压压力将水星白天磁层压缩到表面的观测
DOI：
10.3847/1538-4357/ab6170
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
M. A. Asad
中科院分区：
文献类型：
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作者：
R. Winslow;N. Lugaz;L. Philpott;C. Farrugia;C. Johnson;B. Anderson;C. Paty;N. Schwadron;M. A. Asad
众所周知，水星的磁层受到行星际日冕物质抛射(ICME)内部增强的冲压和磁场的影响。在这里，我们报告了ICME将水星的日侧磁层压缩到表面的详细观测。2013年11月29日从太阳发射的一个快速CME首先在11月30日撞击了围绕水星运行的水星表面、空间环境、地球化学和测距(信使)宇宙飞船，然后在12月1日撞击了近1Au的STEREO-A。在ICME撞击后，信使号保持在太阳风中，航天器向内和向北向水星表面飞行，直到它到达并通过离水星最近的接近(371公里高度)，而没有进入磁层。在到达400公里高度和84°N纬度的行星黑夜之前，磁层穿越终于发生了1分钟，这表明该轨道上没有白天的磁层。此外，由于磁层压缩，信使号此时测得的峰值磁场比ICME之前和之后轨道上测得的值高出40%。使用水星上的替代方法和STEREO-A上的测量，我们证明了与ICME相关的极高的冲压足以使水星的弱磁层坍塌。因此，ICME等离子体很可能与水星的表面发生了相互作用，这从外圈中增强的钠离子中得到了证明。水星日侧磁层的坍塌对围绕M矮星的近距离系外行星的宜居性具有重要影响，因为这种事件可能会对这些系统中的行星大气损失做出重大贡献。
Mercury’s magnetosphere is known to be affected by the enhanced ram pressure and magnetic fields inside interplanetary coronal mass ejections (ICMEs). Here we report detailed observations of an ICME compressing Mercury’s dayside magnetosphere to the surface. A fast CME launched from the Sun on 2013 November 29 impacted first the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, which was orbiting Mercury, on November 30 and later STEREO-A near 1 au on December 1. Following the ICME impact, MESSENGER remained in the solar wind as the spacecraft traveled inwards and northwards toward Mercury’s surface until it reached and passed its closest approach to the planet (at 371 km altitude) without crossing into the magnetosphere. The magnetospheric crossing finally occurred 1 minute before reaching the planet’s nightside at 400 km altitude and 84°N latitude, indicating the lack of dayside magnetosphere on this orbit. In addition, the peak magnetic field measured by MESSENGER at this time was 40% above the values measured in the orbits just prior to and after the ICME, a consequence of the magnetospheric compression. Using both a proxy method at Mercury and measurements at STEREO-A, we show that the extremely high ram pressure associated with this ICME was more than high enough to collapse Mercury’s weak magnetosphere. As a consequence, the ICME plasma likely interacted with Mercury’s surface, evidenced by enhanced sodium ions in the exosphere. The collapse of Mercury’s dayside magnetosphere has important implications for the habitability of close-in exoplanets around M dwarf stars, as such events may significantly contribute to planetary atmospheric loss in these systems.