A light gas gun at the University of Kent will fire projectiles into mineral samples to see how violent impacts alter the water they contain. Scientists analysing meteorites and returned asteroid samples rely on hydrogen measurements in the mineral apatite and in glass to trace where water in the inner Solar System came from. But every extraterrestrial rock has been battered by hypervelocity impacts, and no one knows whether those shocks change the hydrogen content or its isotopic ratio. If shock alters the signal, then decades of planetary water estimates could be wrong. This project will fire terrestrial apatite and basalt glass with known water contents under vacuum and under a simulated Mars-like atmosphere, then measure how hydrogen abundance and deuterium/hydrogen ratios shift at different shock pressures. The results will provide a correction factor for interpreting water in samples from the Moon, Mars, and asteroids. This is fundamental science with no immediate practical application, but understanding how water is retained on rocky bodies directly informs models of planet formation and habitability—both in our Solar System and for exoplanets.
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Meteorites and returned samples (e.g., from asteroids, the Moon, Mars and other differentiated bodies) have been extensively analysed to determine the source and abundance of water delivered to the early inner Solar System. These studies are largely based on hydrogen abundance and D/H ratio measurements of the mineral apatite [Ca5(PO4)3(F, Cl, OH)] and/or glass melt inclusions in these rocks. However, extraterrestrial samples have all experienced some degree of hypervelocity impact processing, potentially effecting change on their hydrogen inventory. It is therefore vital to understand how hydrogen is affected by impact processes in order to avoid misinterpretations of the origin and distribution of volatile elements in the Solar System. The aim of this research is to determine how impact processes affect hydrogen inventories (abundance and D/H ratios) within apatite and glass on airless planetary bodies and under martian atmospheric conditions. This aim will be achieved by: Objective 1: Simulating impact shock pressures on terrestrial apatite and basaltic glass standards with varying known water contents, using the University of Kent Light Gas Gun (LGG). One set of experiments will be performed under vacuum to simulate the environment on airless bodies, and one set will be performed under a simulated D-enriched martian atmosphere. Objective 2: Determining the precise shock stage (S1-6, and GPa equivalent) produced in the most shocked and less shocked parts of each experimental standard, via electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) analyses. Objective 3: Identify how/if hydrogen abundance and D/H ratio has changed within the most shocked and less shocked parts of each experimental standard, using stepwise pyrolysis mass-spectrometry at the Scottish Universities Environmental Research Centre (SUERC). Objective 4: Collate the above results to determine the extent of potential change in hydrogen abundance and D/H ratio for a given shock stage in both apatite and glass on airless bodies and under martian atmospheric conditions. Knowing how, when and from where volatiles were delivered is fundamental to our understanding of rocky planet formation, evolution and habitability, both within and beyond our Solar System. This research will lead to a better understanding of hydrogen mobility during impact shock, and thus will provide a substantial advancement in our knowledge of water retention on rocky bodies throughout solar system(s) formation and evolution.
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