Planetary auroras: a universal perspective

许多不同的宇宙体，从小行星到大质量恒星，都拥有磁场。地球的磁场保护我们免受有害的太阳风(太阳发出的粒子流)的影响，木星是太阳系中最大的天体，而系外行星的磁场可能提供一种新的探测方法。它们特别值得研究，因为对这许多不同类型天体的分析是相互启发的，即我们可以通过研究离我们家更近的物体来了解更多关于遥远天体的信息，反之亦然。因此，这一提议是通过一种普遍存在的现象--北极光，或称极光--对太阳系和其他星系中行星磁场的动力学进行全面研究。太阳系其他行星上的极光可以用哈勃太空望远镜(HST)来研究，它们就像上层大气中的电视屏幕，告诉我们能量是如何通过行星磁场控制的空间流动的。我们对土星磁场的了解存在一些根本性的空白。当行星自转时，大多数行星的磁场就像倾斜的旋转顶端一样摆动。土星的独特之处在于它没有，但奇怪的是，许多与磁场相关的现象，如极光，在自转周期附近脉动。这可能是由于夏季和冬季极地高层大气条件的不同，但HST只观测到了南部极光。此外，土星的高层大气比模型预测的要热得多。我将获得北极光的HST图像，结合卡西尼号的现场测量，将提供解决这些问题所需的数据。尽管大多数行星的磁场存在“自转顶部”的摆动，但描述木星快速自转如何产生极光的模型假设根本没有摆动，即关于自转轴的经向对称。这是一个基本的遗漏，因为木星的极光显然不是纵向对称的，而木星是各种脉冲发射的来源，这些脉冲发射肯定是由纵向不对称造成的。因此，我将开发包括这种不对称性的模型，并确定磁场的形状和极光过程是如何相互依赖的。这些对木星倾斜磁场动力学的研究将成为开发天王星和海王星高度不对称磁场模型的垫脚石，人们对此知之甚少。因此，这些模型将发现这些神秘的磁场是如何工作的。已发现数百颗质量与木星大致相当的行星围绕其他恒星运行。这些行星中的大多数都非常靠近恒星的轨道，因为目前的探测方法最擅长发现距离恒星很近的行星。据推测，这些行星受到恒星风的冲击，可以产生足以在数十光年内探测到的极光无线电波。然而，我最近证明，以土星轨道距离绕热恒星运行的快速旋转的行星同样可以产生这种可探测到的射电辐射。因此，我将开发这个模型，以准确地确定这类目前被忽视的行星的哪些配置是可以探测到的，并搜索射电望远镜数据以进行探测。探测围绕其他恒星运行的行星的磁层具有潜在的生命友好性，这一可能性特别令人兴奋，对更广泛的社会具有重大意义。

Many different cosmic bodies, from small planets to massive stars, possess magnetic fields. The Earth's magnetic field protects us from the harmful solar wind (a stream of particles emitted from the Sun), Jupiter's is the largest object in the solar system, and those of exoplanets may offer a new detection method. They are particularly interesting to study since the analyses of these many different types of body are mutually illuminating, i.e. we can learn much about distant astrophysical bodies by studying objects much closer to home, and vice versa. This proposal is thus a holistic study of the dynamics of planetary magnetic fields in our solar system and others, through a ubiquitous phenomenon: the 'northern lights', or aurora. Auroras on other planets in the solar system can be studied with the Hubble Space Telescope (HST), and they act as 'TV screens' in the upper atmospheres telling us how energy flows through the space controlled by the planets' magnetic fields. There are some fundamental gaps in our knowledge about Saturn's magnetic field. Most planets' magnetic fields wobble like tilting spinning tops as the planets spin. Saturn's is unique in that it does not, and yet strangely many phenomena associated with the magnetic field, like the aurora, pulse near the spin period. This could be due to a difference in conditions in the upper atmosphere at the summer and winter poles, however HST has only ever observed the southern auroras. In addition, Saturn's upper atmosphere is much hotter than models predict. I will obtain HST images of the northern auroras, which, in conjunction with in situ Cassini measurements, will provide the data required to resolve these problems. Despite the 'spinning top' wobble in most planets' magnetic fields, the models which describe how auroras are generated by the rapid rotation of Jupiter assume no wobble at all, i.e. symmetry in longitude about the spin axis. This is a fundamental omission, since Jupiter's auroras are clearly not longitudinally symmetric, and Jupiter is the source of various pulsing emissions which must be caused by a longitudinal asymmetry. I will thus develop the models to include this asymmetry, and also determine how the shape of the magnetic field and auroral processes are interdependent. These studies of the dynamics of Jupiter's tilted magnetic field will act as stepping stones toward developing models for the highly asymmetric magnetic fields of Uranus and Neptune, about which very little is known. These models will therefore make discoveries about how these enigmatic magnetic fields work. Many hundreds of planets of roughly Jupiter's mass have been discovered orbiting other stars. Most of these orbit very close to the star, since present detection methods are best at finding close planets. The buffeting of these planets by stellar winds has been suggested to generate auroral radio waves powerful enough to be detected across tens of lightyears. However, I have recently shown that rapidly-spinning planets orbiting hot stars at the equivalent of Saturn's orbital distance could equally generate such detectable radio emissions. I will thus develop this model to determine exactly what configurations of this presently-overlooked class of planet are detectable, and also search radio telescope data for detections. The possibility of detecting potentially life-friendly magnetospheres of planets orbiting other stars is particularly exciting and of significant relevance to wider society.