Comparative planetary infrared aurorae

行星极光，就像地球的北极光和南极光一样，是由高能带电粒子沿着行星的磁力线从周围的空间环境流入高层大气形成的。然而，这些带电粒子来源的不同意味着不同行星的极光之间存在着相当大的差异。在地球上，极光受磁场和太阳风之间相互作用的影响。木星和土星比地球质量大得多，自转速度也比地球快，因此这些行星的磁场要强得多。这导致了连接行星和附近太空环境的电流，使其不受太阳风的影响。天王星的磁场与地球的磁场更加不同，这也会产生与行星相连的电流。这些洋流产生的极光与地球上常见的极光有很大不同。我们的工作是使用地面和土星轨道上的望远镜，在红外波段观测气体巨星的极光。这不仅允许我们测量整个行星上极光的变化亮度，而且还可以显示行星上层大气中的离子如何由于引起极光的洋流而运动。通过这些观测，我们已经能够证明，气体巨星上看到的极光实际上是由各种当前系统产生的，其中一些与地球上的太阳风有关，另一些与当地空间环境中的过程有关。然而，我们也观察到了许多仍未被这两个过程解释的特征。在这个研究计划中，我们打算利用对气态巨型极光的观测，通过更好地直接描述这些极光的特征，来显著提高我们对导致这些极光形成的不同过程的理解。在过去的一年里，为支持2007年2月的“新地平线”飞越，对木星和土星的极光进行了一个重要的观测方案。这包括哈勃太空望远镜拍摄的高细节紫外线(UV)图像，以及地面红外(IR)活动，这将使我们能够首次直接将精细图像与光谱数据进行比较。作为国际天王星赤道观测活动的一部分，我们还拍摄了有史以来第一张气态巨星高层大气的图像，修正了透过地球大气层观察的扭曲效应。这使我们能够以前所未有的精确度观测天王星的高层大气。除此之外，我们还领导了对卡西尼号航天器上的VIMS仪器拍摄的土星极光新图像的分析，该仪器位于土星环绕地球的轨道上。这些让我们看到了极光，向我们展示了一套全新的发射，看起来不像以前在土星或任何其他行星上看到的任何东西。我们打算分析这一新的丰富数据，以了解不同行星的极光之间的差异。通过显示太阳风对这些行星上极光的控制程度，并将其与我们对周围空间环境的了解进行比较，将可能理解太阳风对行星上层大气的影响如何随着行星构型的变化而变化。其中一些影响太小，在地球上无法正确区分，但在其他行星上要强大得多，而且占主导地位。因此，我们的观测也将使我们能够更好地了解能量如何从太阳流向地球的细节。

Planetary aurorae, like the Earth's aurora borealis and aurora australis, are formed by energetic charged particles streaming along the planet's magnetic field lines into the upper atmosphere from the surrounding space environment. However, differences in the source of these charged particles means there are considerable variations between the aurora of different planets. On Earth's, the aurorae are dominated by the effect of interactions between the magnetic field and the solar wind. Jupiter and Saturn are far more massive and also rotate more quickly than the Earth and as a result the magnetic fields of these planets are much stronger. This results in currents that connect between the planet and the nearby space environment, shielded from the solar wind. Uranus has a magnetic field that is even more different to the Earth's and this too produces currents that connect with the planet. These currents produce aurora that differ significantly from those usually seen on Earth. Our work uses telescopes on the ground and in orbit around Saturn to observe the aurorae of the gas giants at infrared wavelengths. This allows us to not only measure the varying brightness of the aurora across the planet, but also show how the ions in the upper atmosphere of the planets move as a result of the currents which cause the aurora. Using these observations we have been able to show that the aurorae seen on the gas giants are, in fact, produced by a variety of current systems, some connected to the solar wind as at Earth and others with processes within the local space environment. However, we have also observed many features that remain unexplained by either process. In this programme of research we intend to use observations of the gas giant aurorae to significantly improve our understanding of the different processes that lead to the formation of these aurora by better characterising them directly. In the past year, a significant programme of observations were made of the aurorae of both Jupiter and Saturn, in support of the New Horizons flyby in February 2007. This consist of highly detailed ultraviolet (UV) images taken by the Hubble Space Telescope, together with a ground-based infrared (IR) campaign, which will allow us to directly compare the fine-scale images directly with the spectral data for the first time. As a part of the international Uranus at Equinox observing campaign, we also took the first-ever image of the upper atmosphere of a gas giant, correcting for the distortional effect of looking through the Earth's atmosphere. This allows us to observe the upper atmosphere of Uranus at an unprecedented accuracy. In addition to this, we have led the anaylsis of new images of Saturn's aurora taken by the VIMS instrument aboard the Cassini spacecraft, in orbit around around the planet. These have given us views of the aurora, presenting us with a whole new set of emission that looks unlike anything seen before on Saturn, or any other planet. We intend to analyse this new wealth of data to understand the differences between the aurorae of different planets. In showing the extent to which the solar wind controls the aurora on each of these planets and comparing this with what we know about the surrounding space environment, it will be possible to understand the way solar wind influences on a planet's upper atmospheres change with the planetary configuration. Some of these effects, that are too small to properly distinguish on the Earth, are far more powerful and dominant on other planets Thus, our observations will also allow us to better understand the details of how energy flows from the Sun to the Earth.