The History of Water at Lyot Crater, Mars: Possible Surface Manifestations of Ancient Groundwater and/or Recent Climate Change

Brooker, Laura (2019). The History of Water at Lyot Crater, Mars: Possible Surface Manifestations of Ancient Groundwater and/or Recent Climate Change. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f419

Abstract

This thesis explores the history of water in and around Lyot crater (50°N, 30°E), a ~215 km impact crater on Mars. The primary research objective is to understand whether the landscape records the actions of both ancient subsurface water and recent atmospherically-derived water, to help determine whether the study area contains material of astrobiological interest. I first mapped the distribution of landforms and surface types potentially indicative of water and/or ice across the interior and ejecta blanket of Lyot crater. I identified landforms of particular interest to this study – fluvial channels, fan deposits and clastic polygonal networks – and recognised that the majority of fluvial features are within the crater interior. Using geomorphological mapping, I constructed a stratigraphic history of the units and landforms in the crater interior, providing context for the fluvial activity. Morphological study of the small channels and fan deposits suggests they have a subaerial origin, with water sourced from the melting of atmospherically-deposited ice-rich material, and reveals the presence of potential standing bodies of water within closed basins during the mid- to late- Amazonian. Clastic polygonal networks in the outer ejecta blanket were analysed: their spatial distribution indicates a genetic link to the impact event. A mechanism is proposed whereby thermal contraction cracks in ice-rich ground are modified to form angular clastic margins. Impact models, using iSALE hydrocode, show a maximum exhumation depth of 10-12 km for the Lyot-forming event, indicating that the cryosphere was penetrated and that outflow channels to the north could be groundwater related. Furthermore, pore ice/water in the inner ejecta might have been stable as liquid water, and later flowed into the region where the polygons formed. These results indicate a history of both ancient subsurface water and recent atmospheric water, and that Lyot Crater is a site of significant astrobiological interest.

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