Determination of sputtering and desorption cross sections for metal species relevant to the exosphere of Mercury & other airless bodies: Laboratory measurements

水星表面覆盖着一层主要由硅酸盐矿物组成的岩石外壳，白天的温度比地球上的温度要高得多。它非常稀薄的大气层主要是由太阳风与行星表面的相互作用，以及流星的轰击和行星地壳内元素的放射性衰变产生的。这种土壤衍生的“外逸层”含有Na、K、Ca、Al、Mg、Fe和Mn等金属挥发性物质，这些物质已被地球上的望远镜和轨道航天器观测到。对于钠和钾从地表释放的情况，只有很少的实验测量是可用的，而对于所有金属挥发种类，没有系统的数据。这个团队将提供关键的实验室测量，以解释水星外逸层的观测结果，(2)改进外逸层的理论模型，(3)为尚未观测到的无空气天体（如小行星或彗星）提供预测。在这项资助的每一年，PI将资助两名社区学院转学生注册为STEM专业，在夏季进行行星科学研究。该团队将对模拟水星表面喷射出的金属挥发性物质的热解吸、紫外光解吸和离子溅射截面进行实验室测量。在与汞相关的条件下，将在实验室中测量矿物表面和碳质陨石中吸附和固有（并入晶格中的）金属挥发物[Na， K, Ca, Al, Mg， Fe和Mn]的重要挥发物的横截面。测量将作为温度、衬底材料、衬底粗糙度和离子辐照历史的函数来执行。1 keV/am太阳风的主要成分H+和He+将被用作太阳风类似物，允许系统地研究化学溅射；2 keV H2+也将用于检查任何分子溅射效应。莱曼- α或其他紫外光子将用于光子激发解吸测量。x射线光电子能谱将用于量化金属挥发物的表面丰度，用于解吸和溅射测量，而喷射出的中性物质和/或离子将由质谱仪测量。这种技术组合将提供补充性的定量信息，说明表面消耗是否完全是由于损失到真空中，还是扩散到大块中起作用。目标是确定金属挥发物与行星风化层的表面结合能，并定量评估形成水星和其他无气天体外逸层的每种物理机制的相对重量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The surface of Mercury is covered by a rocky crust made up mostly of silicate minerals, and daytime temperatures are significantly warmer than those found on Earth. Its very thin atmosphere is generated mostly by the interaction of the solar wind with the planetary surface, as well as bombardment by meteors and the radioactive decay of elements within the planet’s crust. This soil-derived “exosphere” contains metal-volatile species of Na, K, Ca, Al, Mg, Fe, and Mn, which have been observed by telescopes on Earth and by orbiting spacecraft. There are only a few experimental measurements for the release of sodium and potassium from the surface that are available, with no systematic data for all metal-volatile species. This team will provide critical laboratory measurements needed to interpret observations of Mercury’s exosphere, (2) improve theoretical models of the exosphere, and (3) provide predictions for as yet unobserved airless bodies, such as asteroids or comets. During each year of this grant, the PI will sponsor two Community College transfer students enrolled as STEM majors to spend the summer performing research on Planetary Science. The team will carry out laboratory measurements of thermal desorption, UV photo-desorption, and ion-sputtering cross sections for metal-volatile species ejected from a simulated Mercurian surface. Cross sections for important volatile species will be measured in the laboratory for both adsorbed and intrinsic (incorporated into the lattice) metal volatiles [Na, K, Ca, Al, Mg, Fe, and Mn] from mineral surfaces and carbonaceous meteorites under conditions relevant to Mercury. Measurements will be performed as a function of temperature, substrate material, substrate roughness, and ion irradiation history. 1 keV/am H+ and He+, the primary components of the solar wind, will be used as solar-wind analogs, allowing systematic investigation of chemical sputtering; 2 keV H2+ will also be used to examine any molecular sputtering effects. Lyman-alpha or other UV photons will be used for photon-stimulated desorption measurements. X-ray photoelectron spectroscopy will be used to quantify the surface abundance of metal volatiles for desorption and sputtering measurements, and the ejected neutral species and/or ions will be measured by a mass spectrometer. This combination of techniques will provide complementary quantitative information on whether surface depletions are due exclusively to loss into vacuum, or if diffusion into the bulk plays a role. The goal is to determine the surface binding energies for the metal volatiles to the planetary regolith, and quantitatively evaluate the relative weight for each of the physical mechanisms contributing to the exospheres of Mercury and other airless bodies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.