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

水星的表面覆盖着一层主要由硅酸盐矿物组成的岩石地壳，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。只有少数几个实验测量钠和钾从表面释放，没有系统的数据，所有金属挥发性物种。该团队将提供解释水星外逸层观测所需的关键实验室测量，（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。在每年的补助金期间，PI将赞助两名社区学院转学生作为STEM专业入学，以度过夏季进行行星科学研究。该小组将对从模拟水星表面喷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。重要的挥发性物质的横截面将在实验室中测量吸附和内在的（纳入晶格）金属挥发物[Na，K，Ca，Al，Mg，Fe和Mn]从矿物表面和碳质陨石的条件下有关汞。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进行。1 keV/am的H+和He+，太阳风的主要成分，将被用作太阳风的类似物，允许化学溅射的系统研究; 2 keV的H2+也将被用来检查任何分子溅射效应。莱曼-α或其他UV光子将用于光子激发解吸测量。X射线光电子能谱法将用于量化金属挥发物的表面丰度，以进行解吸和溅射测量，喷射的中性物质和/或离子将通过质谱仪测量。这种技术的结合将提供补充的定量信息，表面损耗是否完全是由于进入真空的损失，或如果扩散到散装发挥作用。其目标是确定金属挥发物与行星风化层的表面结合能，并定量评估导致水星和其他无空气天体外逸层的每种物理机制的相对权重。该奖项反映了NSF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.