Shock Wave Studies of Liquids in Earth's Core and Mantle

该奖项将支持在地球深部压力-温度条件下对熔融岩石和金属进行实验性冲击波测量。冲击波实验利用受控的高速碰撞在短时间内产生高压和高温，从而可以独特地测量地球物质对破坏、高速变形和地球下地幔和地核等条件的反应。这些数据是支持下地幔结构、深部碳循环、早期陆生岩浆海洋演化和地核组成的下一代模型所必需的。熔融物质是理解行星演化和结构的核心，但我们对它们的理解落后于对固体的理解，因为液体更复杂，更难以研究。来自这些激波实验的数据通常是在极端压力下验证液体结构和动力学原子模型的唯一实验数据。这项工作利用了与劳伦斯利弗莫尔国家实验室的合作，利用能源部冲击物理小组的专业知识来解决地球物理问题，反过来，在这项工作中所做的测量和开发的方法不仅在实验地球物理学中，而且在凝聚态物理和更广泛的冲击压缩社区中都将产生广泛的影响。该项目包括培训青年科学家和通过电视特别节目进行宣传。该项目结合了技术进步，使新的实验、更极端的条件、更高精度的结果和更快的周转时间成为可能。冲击温度测量技术的进步，将不确定度从~500 K降低到~30 K，将用于观察受冲击的硅酸盐液体的温度。高压缩条件下硅酸盐液体（纯SiO2）热容的唯一实验约束表现出极大的复杂性；在液体中测量激波温度确定了该热容并完成了状态方程的描述。测量激波温度的实验也可以配置为测量激波液体状态下的声速，这定义了状态方程的高阶约束，并允许对硅酸盐液体的Mie-Gruneisen公式进行关键测试。沿着实际的外核绝热器测量液态铁合金的声速和密度，将使用冲击-释放和冲击-斜坡加载路径的组合，将熔融铁和铁合金样品带到外核，而不需要预热或外推。等熵实验将使外核中声速随深度的明显梯度成为对其组成的新约束。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。

This award will support experimental shock wave measurements of molten rocks and metals at the pressure-temperature conditions of the deep Earth. Shock wave experiments use controlled high-speed collisions to generate high pressure and temperature for a short time, allowing unique measurements of the response of Earth materials to damage, high-speed deformation, and conditions like those in the lower mantle and core of the Earth. These data are needed to support next-generation models of lower mantle structure, the deep carbon cycle, evolution of an early terrestrial magma ocean, and the composition of the Earth's core. Molten materials are central to the understanding of planetary evolution and structure, but our understanding of them lags our understanding of solids because liquids are more complex and more difficult to study. Data from these shock wave experiments is often the only experimental data available at extreme pressure for validation of atomistic models of liquid structure and dynamics. This work leverages collaboration with Lawrence Livermore National Laboratory to exploit the expertise in the Department of Energy's shock physics group for geophysical problems and, in turn, the measurements made and methods developed in this work will have wide impact not only in experimental geophysics but also in condensed matter physics and the broader shock compression community. The project includes training of young scientists and outreach through television specials.The project incorporates technical advances that enable new experiments, more extreme conditions, higher precision results, and faster turn-around time. Advances in shock temperature measurement technique, reducing uncertainty from ~500 K to ~30 K, will be used to look at temperatures of shocked silicate liquids. The one experimental constraint on the heat capacity of a silicate liquid (pure SiO2) at high compression shows great complexity; measuring shock temperature in liquid defines this heat capacity and completes the description of the equation of state. Experiments that measure shock temperature can also be configured to measure the sound speed in the shocked liquid state, which defines high-order constraints on the equation of state and allows a key test of the Mie-Gruneisen formulation for silicate liquids. Measurement of sound speeds and densities of liquid Fe alloys along actual outer core adiabats will use a combination of shock-and-release and shock-and-ramp loading paths to bring molten Fe and Fe-alloy samples to the outer core isentrope without the need for pre-heating or extrapolation. Isentropic experiments will make the well-defined observed gradient in sound speed with depth in the outer core a new constraint on its composition.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.