Exploring clouds and gaseous abundances in the atmospheres of Uranus and Neptune

探索天王星和海王星大气中的云和气体丰度

• 批准号: 2889689
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2889689
• 关键词: Exploring; clouds; gaseous; abundances; atmospheres

Uranus and Neptune, known as the "Ice Giants" are amongst the most mysterious and poorly understood planets in our solar system. The poles of Uranus are tipped over by an extraordinary 98 degrees (compared with an obliquity of 23.5 degrees for the Earth) leading to enormous annual variations in solar forcing, with the poles annually receiving more sunlight per unit area than the equator! In contrast, Neptune's obliquity of 29 degrees appears much less anomalous. The Voyager 2 fly-bys in 1986 and 1989 provided our only close-up views of these worlds and revealed that Uranus is in almost perfect radiative balance with the Sun, while Neptune emits thermally more than 2.5 times the solar radiation it receives! Perhaps as a result of this imbalance, the atmospheric circulation of Uranus was found to be rather quiescent, while that of Neptune was extraordinarily dynamic and active. More than a quarter of a century later, the spatial resolution of ground-based telescopes has been transformed by the development of adaptive optics. The activity of Uranus's atmosphere has been seen to increase dramatically through its equinox in 2007, while Neptune's atmosphere shows enormous changes in cloud activity. We have been monitoring and these developments with an extensive programme of near-infrared ground-based observations at the Gemini-North Telescope in Hawai'i and ESO's Very Large Telescope in Chile. Near infrared reflectance spectroscopy enables us to determine the vertical and horizontal distribution of cloud and gaseous abundances in these atmospheres, using our world-leading NEMESIS retrieval code. Recent highlights include: 1) the first positive detection of hydrogen sulphide in the atmosphere of Uranus (Irwin et al., 2018; https://doi.org/10.1038/s41550-018-0432-1) and probable detection in Neptune's atmosphere (Irwin et al., 2019; https://doi.org/10.1016/j.icarus.2018.12.014); 2) the first ground-based detection of methane latitudinal variability in Neptune's atmosphere (Irwin et al., 2021; https://doi.org/10.1016/j.icarus.2020.114277); and most recently 3) a 'holistic' cloud model that matches the observed reflectivity spectra of both Uranus and Neptune from 0.3 to 2.5 microns (Irwin et al., 2022; https://doi.org/10.1029/2022JE007189), and can explain the difference in colour between these two worlds.The aim of this project is to develop our ground-based visible and near-infrared observing programme and combine existing observations with recent observations made with the James Webb Space Telescope, and also propose and conduct future observations. This project is particularly timely given that a dedicated space mission to one of the Ice Giants was recommended by the 2022 NASA Decadal Survey in Planetary Science. The work will use the newly-developed Minnaert analysis scheme of Irwin et al. (2019) (https://doi.org/10.1016/j.icarus.2018.12.014), which enables efficient fitting of both the mean spectra at target latitudes and their limb-darkening properties, which constrains the particle scattering properties much more strongly. In addition, the work will use a newly-developed image deconvolution scheme (Irwin et al., 2022; https://doi.org/10.1029/2022JE007189) which improves the spatial resolution and allows better discrimination between different latitudes and also the search for discrete atmospheric features. Finally, there is a possibility in the project to implement a more Bayesian analysis of the observations via transcription of the scattering code (currently written in Fortran) to python and using a nested sampling approach that is already used by NEMESIS for exoplanet retrievals.

天王星和海王星，被称为“冰巨人”是我们太阳系中最神秘，最鲜为人知的行星之一。天王星的杆子被倾斜了98度（地球的倾斜度为23.5度），导致太阳能强迫的年度变化巨大，而每年的杆子比赤道接收到每单位面积的阳光更多！相比之下，海王星的倾斜度为29度似乎不那么异常。 1986年和1989年的Voyager 2飞行速率提供了我们对这些世界的唯一特写景观，并透露，天王星与太阳的辐射平衡几乎是完美的辐射平衡，而Neptune的热量超过了它接收到的太阳辐射的2.5倍以上！也许由于这种不平衡，天王星的大气环流被发现相当静止，而海王星的循环却是极具动态和活跃的。四分之一多世纪后，自适应光学器件的发展改变了地面望远镜的空间分辨率。 2007年，已经看到天王星大气的活性通过其春分大大增加，而海王星的大气层显示出云活动的巨大变化。我们一直在监视这些发展，并通过在夏威夷的双子座北望远镜和ESO在智利的非常大的望远镜的Gemini-North望远镜上进行了广泛的近红外地面观测计划。近红外反射光谱使我们能够使用我们的世界领先的克星检索代码来确定这些大气中云和气态丰度的垂直和水平分布。最近的亮点包括：1）在天王星大气中硫化氢的首次阳性检测（Irwin等，2018; https：//doi.org/10.10.1038/s41550-018-0432-1）和在Neptune的大气中可能检测到可能的检测（Irwin Et。 https://doi.org/10.1016/j.icarus.2018.12.014）; 2）在海王星大气中对甲烷纬度变异性的第一个基于地面的检测（Irwin等，2021; https：//doi.org/10.1016/j.icarus.2020.114277）;最近3）一个“整体”云模型，该模型与天王星和海王星的反射光谱从0.3到2.5微米匹配（Irwin等，2022; https：//doi.org/10.10.1029/2029/2029/20222JE007189），并可以在这两个世界之间进行近距离差异。将现有观察结果与詹姆斯·韦伯太空望远镜进行的最新观察结果结合在一起，还提出和进行未来的观察结果。尤其是及时的，鉴于2022年NASA年代际科学调查推荐了一家冰巨头的专门空间任务。这项工作将使用Irwin等人的新发达的Minnaert分析方案。 （2019）（https://doi.org/10.1016/j.icarus.2018.12.014），该）可以有效地拟合目标纬度处的平均光谱及其肢体变形的特性，从而限制了粒子散射的性能。此外，这项工作将使用新开发的图像解卷积方案（Irwin等，2022; https：//doi.org/10.1029/2022JE007189），可改善空间分辨率，并允许更好地识别不同的时间表，并搜索搜索离散的大气特征。最后，该项目有可能通过转录散射代码（目前用fortran编写）到Python进行更多贝叶斯分析，并使用nemesis已使用的嵌套采样方法来用于系外行星的检索。