The Nature of Europa's Surface and Ocean from New Infrared Spectroscopy

木星的卫星木卫二可能拥有一个大约100公里深的全球海洋，其体积是地球上所有液态水的2到3倍。尽管伽利略号航天器进行了近十年的观测，但仍然不清楚木卫二是否只是一个被动的冰壳，表面有一层薄薄的活性化学物质，或者是一个地质活跃的天体，拥有化学物质丰富的海洋。解决这个问题的关键之一是确定冰表面和海洋内部化学之间的关系。最近的模型表明，由离子轰击产生的水合硫酸在后半球应该是丰富的，而由海洋蒸发沉积的水合盐在其他地方更占主导地位。伽利略数据的光谱分辨率不足以详细限制模型;但现代红外光谱仪在大型地面望远镜上配备自适应光学系统，能够绘制表面化学。主要研究员和合作者将使用凯克望远镜上的自适应光学系统观察木卫二，以获得从近红外到热红外前所未有的高光谱分辨率和中等空间分辨率，并将对木卫二表面进行化学测绘，识别盐和辐射产物并确定其空间分布。他们将构建木卫二表面化学物质来源和汇的综合模型，解开本土和外源物质，并开始探索冰壳下看不见的海洋的化学成分。该项目将构成博士学位。一名研究生的论文工作，一名本科生将通过暑期本科生研究奖学金计划参与该项目。首席研究员将通过各种外联活动向公众宣传研究结果。

Jupiter's moon Europa may harbor a global water ocean of approximately 100 km in depth, having 2 to 3 times the volume of all the liquid water on Earth. Despite almost a decade of observations from the Galileo spacecraft, it is still not clear whether Europa is merely a passive ice shell with a thin surface layer of active chemistry, or a geologically active body with a chemically rich ocean. One key to resolving the issue is determining the relationship between the icy surface and the interior ocean chemistry. Recent models suggest hydrated sulfuric acid created by ion bombardment should be abundant in the trailing hemisphere, with hydrated salts deposited by ocean evaporation more dominant elsewhere. Galileo data are of insufficient spectroscopic resolution to constrain the models in detail; but modern infrared spectrographs with adaptive optics systems on large ground based telescopes are capable of mapping the surface chemistry. The Principal Investigator and collaborators will observe Europa using the adaptive optics system on the Keck telescope to obtain unprecedentedly high spectral resolution and moderate spatial resolution from the near infrared through the thermal infrared, and will chemically map the surface of Europa, identifying salts and radiation products and determining their spatial distributions. They will construct a comprehensive model of the sources and sinks of chemical species on Europa's surface, disentangle indigenous and exogenous materials, and begin to explore the chemical composition of the unseen ocean beneath the icy crust. The project will constitute the Ph.D. dissertation work of a graduate student, and an undergraduate student will be involved in the project through the Summer Undergraduate Research Fellowship program. The Principal Investigator will communicate research results to the public through a variety of outreach activities.