Characterisation of Clay-bearing and Fractured terrain at Oxia Planum, and SPLIT testing on Martian Analogues

This thesis is focused on characterising Oxia Planum, the landing site for the ExoMars 2022 Rosalind Franklin rover. This involved the investigation and mapping out of the sites’ Clay-bearing Unit, as well as digitising the extensive fracture networks present, using visible to near infrared images. Alongside this a prototype geotechnics tool intended for inclusion on a future Mars mission, the Small Planetary Linear Impulse Tool (SPLIT), was tested to determine how it compares to existing geotechnics tools.

The Clay-bearing Unit, consisting of two subunits, was investigated and mapped using the  instruments. This was performed to better understand Colour and Stereo Surface Imaging System (CaSSIS) and High Resolution Imaging Science Experiment (HiRISE) how the Clay-bearing Unit varies over its extent, and if any such variations correlated to other features at the site. It was found that differences between the two subunits are likely due to mineralogical variation rather than differences in surficial cover, with the formation of the subunits occuring before a channel-forming stage of aqueous activity at the site.

Fracture digitisation using HiRISE was also performed, with sites from units at Oxia Planum having their fracture networks digitised and parametrised. These were compared to each other and with sites at Gale Crater; sites on the margins of an unnamed crater within the Vastitas Borealis north polar region; and two Earth-based sites. This indicates that several mechanisms are unlikely to have caused the fracturing seen at Oxia Planum e.g., hydraulic fracturing and thermal fracturing, and identified that the fracturing within the Clay-bearing and Capping Units likely originated during separate fracturing episodes.

SPLIT is an instrument designed to remove the upper layers of a target rock, revealing unaltered material to depths of several centimetres. Testing was carried out on Martian analogue samples in field trials and laboratory tests. These tests were generally successful, defined as removing volumes comparable to that achieved using existing instrumentation, with a smaller power expenditure and in less time. However failure to operate on gypsum due to its friability, as well as on a sandstone and a siltstone sample due to the lack of exploitable weaknesses and low mass of these samples (~3 kg), highlight the mass and material strength limits at which SPLIT can nominally operate.