论文标题
天王星和海王星的上层大气
The upper atmospheres of Uranus and Neptune
论文作者
论文摘要
我们回顾当前对天王星和海王星高层气氛的理解，并探索即将到来的研究这些令人兴奋的行星的机会。冰巨头分别是1986年和1989年仅由单个航天器访问的太阳系中最知名的行星。上层大气在将气氛与磁场中包含的力和过程联系起来方面起着至关重要的作用。例如，极光电流系统可以将带电的颗粒驱动到大气中，从而通过焦耳加热加热。 H $ _3^+$的基于地面的观察结果提供了对高层大气中发生的物理特性和过程的强大远程诊断，而天王星则存在丰富的数据集。这些观察结果跨越了近三十年，并揭示了1992年至2018年之间的高层气氛约为8 k/年，从$ \ sim $ 750 k到$ \ sim $ \ sim $ 500 k $ 500 k。这种趋势的原因尚不清楚，但可能与季节性驱动的变化相关，因为焦耳的加热速率变化而导致的磁性磁性和不断变化，或者可能与磁性持续变化相关。 H $ _3^+$尚未在Neptune发现，但是这一发现为即将到来的设施（例如James Webb Space望远镜（JWST）和下一代30米望远镜的设施提供了低悬挂的水果。自1989年以来，在Neptune中检测H $ _3^+$将首次表征其上层气氛。要充分了解我们需要专用的轨道任务的冰巨头，就像Cassini Spacecraft探索了土星一样。只有通过将磁场的原位观察与轨内遥感结合在一起，我们才能完整地了解能量如何在大气和磁场之间移动。
We review the current understanding of the upper atmospheres of Uranus and Neptune, and explore the upcoming opportunities available to study these exciting planets. The ice giants are the least understood planets in the solar system, having been only visited by a single spacecraft, in 1986 and 1989, respectively. The upper atmosphere plays a critical role in connecting the atmosphere to the forces and processes contained within the magnetic field. For example, auroral current systems can drive charged particles into the atmosphere, heating it by way of Joule heating. Ground-based observations of H$_3^+$ provides a powerful remote diagnostic of the physical properties and processes that occur within the upper atmosphere, and a rich data set exists for Uranus. These observations span almost three decades and have revealed that the upper atmosphere has continuously cooled between 1992 and 2018 at about 8 K/year, from $\sim$750 K to $\sim$500 K. The reason for this trend remain unclear, but could be related to seasonally driven changes in the Joule heating rates due to the tilted and offset magnetic field, or could be related to changing vertical distributions of hydrocarbons. H$_3^+$ has not yet been detected at Neptune, but this discovery provides low-hanging fruit for upcoming facilities such as the James Webb Space Telescope (JWST) and the next generation of 30 metre telescopes. Detecting H$_3^+$ at Neptune would enable the characterisation of its upper atmosphere for the first time since 1989. To fully understand the ice giants we need dedicated orbital missions, in the same way the Cassini spacecraft explored Saturn. Only by combining in-situ observations of the magnetic field with in-orbit remote sensing can we get the complete picture of how energy moves between the atmosphere and the magnetic field.
