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

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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.