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On the Xenology of Comets and Other Primitive Reservoirs in the Solar System

  • Lawton, Thomas
Publication Date
Apr 15, 2021
Manchester eScholar
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The composition of xenon contained within planetary materials can elucidate the conditions within which they were formed and the environments in which they have resided since formation. This work focused on extracting and interpreting xenon isotopic compositions from primitive materials with the development of new methodologies for measuring cometary xenon from 81P/Wild 2, measurement of xenon in primitive volcanic glasses from the lunar interior, and development of modelling software which is used to explore the role of cometary xenon from 67P/Churyumov-Gerasimenko in the delivery of volatiles to the terrestrial planets. The unique combination and development of protocol for Closed-System Stepped Etching (CSSE) with the Refrigerator Enhanced Laser Analyser for Xenon (RELAX) is described, as is a summary of problematic phenomena which may be encountered in its implementation. A noble gas modelling platform, Automaton, is designed, validated, and explained in this work. Automaton can extract the probability and nature of mixtures of xenon components in any given composition, featuring any combination of fractionation before or after mixture. Automaton is employed in determining the role of comet 67P/Churyumov-Gerasimenko in the evolution of the atmospheres of Earth and Mars, and U-Xe. Pristine lunar volcanic glasses are candidates for retaining an indigenous lunar noble gas composition. Individual xenon isotopic compositions of volcanic glasses from Apollo 15 and 17 are reported in this work. Their possible retention of an indigenous lunar noble gas composition and their historical residence on the Moon since crystallisation are discussed. The procedural development and a preliminary analogue experiment for measuring the xenon contained within discrete phases of material collected from comet 81P/Wild 2 by Stardust is described in this work. Results indicate that separately extracted xenon components can be measured by a combination of CSSE and RELAX, so ground truth cometary xenon measurements are possible.

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