CSEDI Research: Investigations of Volatile Acquisition During Earth's Formation

一个适合居住的地球大小的行星的唯一最重要的标准是水和其他挥发物的存在（例如，CO2）对生命至关重要。地球如何获得水是一个激烈争论的研究领域，有许多非常不同的想法正在探索。随着天文学界继续发现大量地球大小的系外行星，这些天体获得挥发物的过程变得至关重要。人们普遍认为，地球的挥发物来源于早期太阳星云的吸入和彗星和小行星的输送。该提案的目标是开发一种基于机器学习的算法，该算法使用多种挥发性元素的丰度和同位素组成，包括H，He，Ne，N，O，Ar，Kr和NH3，以限制这些潜在挥发性来源的相对贡献和时间。这样一来，科学界就可以更好地了解挥发物是如何获得的，以及如何更好地寻找潜在的外星生命。拟议的研究计划是量化在地球历史早期由四个主要来源中的每一个提供给地球的挥发物的数量：来自小行星带的陨石，来自太阳系外围的彗星，来自太阳星云的直接吸入，以及放射性衰变。研究将分三个阶段进行。第一阶段是根据这些来源，建立一个地球吸积过程中挥发性物质获取和损失的综合模型。该模型包括一个原始的大气层来自太阳星云，原地幔与岩浆海洋，和原核心。关键过程包括大气气体交换、岩浆表面的水生成、核幔交换、富含挥发物的地幔岩、彗星、放射性衰变和月球形成事件的修改。第二阶段的地方上的每个源的贡献的界限，使用当今的挥发性物质的丰度和通量的测量作为约束在源的大小反演。要考虑的挥发物是氢、氦、氖、氧、氩、氮、氪和氙的同位素。第三阶段使用机器学习来训练增长模型，以使用来自第二阶段的源幅度来再现观察到的挥发性库存。该项目的预期成果是绘制出地球挥发物的原始来源图，可作为评估遥远类地系外行星可居住性的指南。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 singular most important criterion for a habitable Earth-sized planet is the existence of water and other volatiles (e.g., CO2) critical for life. How Earth acquired its water is a hotly-debated field of research, with a number of very different ideas being explored. As the astronomical community continues to find large numbers of Earth-sized exoplanets, the processes by which such bodies acquire volatiles becomes crucial moving forward. It is generally accepted that Earth’s volatiles were sourced by some combination of ingassing from the early solar nebula and delivery from comets and asteroids. The goal of this proposal is to develop a machine learning-based algorithm that uses the abundance and isotopic compositions of multiple volatile elements, including H, He, Ne, N, O, Ar, Kr and Xe to constrain the relative contributions and timing from these potential volatile sources. In doing so, the scientific community will have a better road-map of how volatiles are acquired and how better to search for potential extraterrestrial life.The proposed research plan is to quantify the amounts of volatiles delivered to the Earth early in its history by each of four major sources: chondrites from the asteroid belt, comets from the outer limits of the solar system, direct ingassing from the solar nebula, and radiogenic decay. The research will be performed in three phases. The first phase is development of a comprehensive model of volatile acquisition and loss during Earth’s accretion based on these sources. The model includes a primitive atmosphere derived from the solar nebula, a proto-mantle with magma oceans, and a proto-core. Critical processes include atmosphere gas exchange, water production at the magma surface, core-mantle exchange, late additions from volatile-rich chondrites, comets, radioactive decay, and modifications by the moon-forming event. The second phase places bounds on the contributions of each source, using measurements of present-day volatile abundances and fluxes as constraints in an inversion for source magnitudes. Volatiles to be considered are the isotopes of hydrogen, helium, neon, oxygen, argon, nitrogen, krypton, and xenon. The third phase uses machine learning to train the accretion model to reproduce the observed volatile inventories using the source magnitudes from the second phase. The expected result of this project is a mapping of Earth’s volatiles to their original sources that can serve as a guide for assessing habitability on distant terrestrial exoplanets.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.