Mass transport and loss in planetary and astrophysical magnetospheres

我想了解带电物质（等离子体）是如何在水星、木星和土星周围的空间中传输的，以及在我们银河系内外的恒星周围传输的。太阳风是一股等离子体流，从太阳吹出，进入行星际空间。一些行星有自己的看不见的磁场，它延伸到太空中很远的地方，就像一个“盾牌”，阻挡太阳风，使大部分太阳风绕着行星偏转。在这个护盾的后面是地球的磁层，就像一个巨大的磁泡。在我们的太阳系之外，也有类似的“风”，吹到恒星附近，产生恒星磁层。行星和恒星的磁层都充满了等离子体。等离子体包裹被“绑”在磁场线上，就像一根绳子上的珠子。等离子体进入磁层有几种方式。它可以从火山卫星上喷发出来，也可以从环中喷出。它也可以从外部进入，当来自太阳风或恒星风的等离子体可以穿透磁层边界（气泡的边缘）时。与任何系统一样，进去的东西必须出来。磁层气泡不可能永远膨胀下去。轨道航天器已经看到物质在磁层内移动并从侧面逃逸。关于带电物质如何在磁场的影响下移动，有几种复杂的理论，但有一个问题：目前的理论无法解释这些观测结果。在磁层的“质量预算”中存在着显著的不平衡。我们大致知道有多少物质进入，但我们看不到它们全部离开。这项工作将找出这些“失踪”的材料去了哪里。它将涉及寻找几个迷人的等离子体过程的近距离证据，包括等离子体交换和磁重联。等离子体交换是一个滑动的、狡猾的过程，在这个过程中，热的、“薄”的等离子体区域悄悄地与冷的、“厚”的等离子体区域交换位置。通过这种方式，厚等离子体可以远离磁层的中心，在其伴随的场线上伸展，并在赤道平面周围形成薄圆盘。重新连接是一个嘈杂和爆炸性的过程，这些拉伸的场线可以戏剧性地断裂，释放出大量储存的能量。我们对地球磁层中的这些过程了解很多，因为有许多卫星在地球附近的太空中飞行，测量这些等离子体运动。然而，我们可以通过将这些知识应用到更远的地方，并探索在其他环境中情况可能有何不同，来了解更多。土星和木星是巨大的行星，旋转非常迅速，由于奇异的火山卫星和环，它们的磁层内有大量的等离子体。另一方面，水星是一个小得多的行星，更容易受到太阳风的影响，因为它离太阳很近。恒星的磁层由于其巨大的尺寸而最引人注目。令人着迷的是，数百万公里外的恒星的能量释放过程可以如此戏剧性，以至于我们可以在地球上用望远镜观察它们！每一颗行星和每一颗星星都有其独特的性质，这就是为什么我发现在这些异国情调和多样化的环境中研究类似的物理学是如此具有挑战性。对我来说，研究一系列环境的回报比只研究一个地方要大得多。

I want to understand how charged material (plasma) is transported in the space around the planets Mercury, Jupiter and Saturn, and around stars in our galaxy and beyond. The solar wind is a stream of plasma that comes off the Sun and blows out into interplanetary space. Some planets have their own invisible magnetic field which stretches huge distances out into space and acts like a "shield", holding off this solar wind flow so that much of it is deflected around the planet. Behind this shield lies the planet's magnetosphere, like a giant magnetic bubble. Outside of our solar system, there are similar "winds", blowing near stars and creating stellar magnetospheres. Both planetary and stellar magnetospheres are full of plasma. Plasma parcels are "tied" to magnetic field lines, like beads on a string. There are several ways for this plasma to get into the magnetosphere. It can erupt from volcanic moons or spew out of the rings. It can also enter from the outside, when plasma from the solar wind or stellar winds can penetrate the magnetospheric boundary (the edge of the bubble). As with any system, what goes in must come out. The magnetospheric bubble cannot inflate forever. Orbiting spacecraft have seen material moving around inside magnetospheres and escaping out the sides. There are several sophisticated theories about how charged material can move around under the influence of a magnetic field, but there is a problem: The current theories cannot explain the observations. There is a significant imbalance in the "mass budget" of magnetospheres. We know roughly how much material goes in, but we don't see it all leave. This work will find out where this "missing" material goes. It will involve searching for close-up evidence of several fascinating plasma processes, including plasma interchange and magnetic reconnection. Plasma interchange is a slippy, slinky process in which regions of hot, "thin" plasma silently swap places with regions of cold, "thick" plasma. In this way, the thick plasma can move away from the centre of the magnetosphere, stretch out on its accompanying field lines, and form a thin disk around the equatorial plane. Reconnection is a noisy and explosive process where these stretched field lines can dramatically break, releasing huge amounts of stored up energy. We know a lot about these processes in Earth's magnetosphere because there are many satellites flying around in space near Earth measuring these plasma motions. However, we can learn much more by applying this knowledge further afield and exploring how the situation may be different in other environments. Saturn and Jupiter are huge planets which rotate very rapidly and have a lot of plasma inside their magnetospheres due to exotic volcanic moons and rings. Mercury on the other hand is a much smaller planet and is much more vulnerable to the effects of the solar wind blowing at it as it is so close to the Sun. Stellar magnetospheres are the most dramatic of all due to their enormous size. It is fascinating to think that energy release processes at stars many millions of kilometres away can be so dramatic that we can observe them with telescopes here on Earth! Every planet and every star has a unique character, which is why I find studying similar physics in these exotic and diverse environments so challenging. The rewards for studying a range of environments for me are much greater than studying one place only.