Extraterrestrial light shows
Extraterrestrial light shows
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外星灯光秀
DOI：
10.1088/2058-7058/29/7/35
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发表时间：
2016
期刊：
影响因子：
0.6
通讯作者：
Badman S
中科院分区：
文献类型：
--
作者：
Badman S
行星科学：极光形成一种磁性“尾巴”。经过一段时间后，这个磁尾变得“加载”场线，磁场经历了爆炸性的重新配置，并将等离子体注入到行星的夜面。其中一些等离子体到达大气层并引起明亮的极光显示。更大的事件可以由太阳活动触发，如高速太阳风或日冕物质抛射（大型太阳等离子体云与磁场）。当其中一个到达地球的磁层时，它可以传递大量的能量，导致异常大而明亮的极光（见图1）。极光通常形成一个圆形，围绕着连接到磁场线环的磁极。通过沿着这些远离行星的磁场线追踪，我们可以发现带电粒子来自磁层的哪里。即使是像极光的颜色这样基本的东西也给了我们丰富的信息。由于不同种类的原子具有不同的能级，能级之间的跳跃决定了能量，从而决定了它们发射的光的波长。例如，北方光中常见的绿色来自地球表面100公里以上的氧原子。当足够多的电子激发了大气层中密度较低的氧气的不同跃迁时，可以看到红色极光，而绿色幕底部的深红色则表明高能电子穿透到大气层更深处并激发了氮分子。
Planetary science: Auroras forming a kind of magnetic “tail”. After an interval in which this magnetic tail becomes “loaded” with field lines, the magnetic field undergoes an explosive reconfiguration and injects plasma back towards the planet on the nightside. Some of this plasma reaches the atmosphere and causes bright auroral displays. Larger events can be triggered by solar activity such as high-speed streams of solar wind or coronal mass ejections (large clouds of solar plasma threaded with magnetic field). When one of these reaches the Earth’s magnetosphere it can transfer a lot of energy, leading to exceptionally large, bright auroras (see figure 1).Auroras normally form a circular shape around the pole connected to a ring of magnetic field lines. By tracing along these magnetic field lines away from the planet, we can find out where in the magnetosphere the charged particles are coming from. Even something as basic as an aurora’s colour gives us a wealth of information. Because different species of atoms have different energy levels, the jumps between levels determine the energy and hence the wavelength of the light they emit. For example, the common green colour in the northern lights comes from oxygen atoms more than 100 km above the Earth’s surface. Red auroras can be seen when enough electrons excite different transitions in the less dense oxygen higher up in the atmosphere, while a deep red at the bottom of the green curtain is indicative of higher-energy electrons penetrating deeper into the atmosphere and exciting nitrogen molecules.