An Investigation into Shock Events on Martian Analogue Minerals using Raman Spectroscopy

In early 2021 both NASA's Mars 2020 and ESA's Rosalind Franklin rovers will land on Mars carrying Raman spectrometers. This will be the first time that a Raman spectrometer has been deployed on another planetary body and both rovers will conduct their mission in regions that contain impact craters and, therefore, it is likely that both missions will encounter samples that have been subjected to shock.

This thesis examines how the Martian environment can potentially influence the Raman spectrum of minerals, which was achieved by examining the effects of temperature and shock.

The first series of experiments investigated the influence of temperature on the Raman spectrum of the three minerals: olivine, quartz, and labradorite. These experiments showed that the Raman peak positions vary based on the temperature of the sample. As the sample temperature was increased, the Raman peak position decreased (at varying rates) for all three minerals, which could lead to the misinterpretation of the exact composition of the minerals samples if not properly corrected for. Further temperature investigations were also conducted into the degree of 'laser heating' generated in samples by the Raman spectrometer during acquisition.

Mineral samples with a range of grain sizes were tested to determine if there is a relationship between the size of the sample and the amount of 'laser heating'. This experiment was not able to detect the presence of any 'laser heating' in any of the samples, however, an experimental procedure has now been developed and can be repeated with smaller, more appropriately sized grains in the future.

The second series of experiments explored the effects of shock on the Raman spectrum of the same three minerals. For this experiment, each of the minerals was impacted using the light gas gun at the University of Kent at a range of velocities (and therefore shock pressures) before being examined using a Raman spectrometer. An attempt was made to determine if the induced changes in the Raman spectrum of the samples could be used as a shock barometer to infer the magnitude of shock experienced by the sample. Results showed that this was generally not possible as much of the shocked material had been excavated during the crater formation process.

It was found that lower speed shots, which merely produced an indentation on the surface of the samples without the loss of material, were better suited to such an investigation. As such, methods of firing the light gas gun at a lower velocity were used. This was done to preserve the experimental procedure across all velocities in order to reduce the chance of introducing systematic errors to the dataset. This required the development of an entirely new firing system known as the electronic burst disk which is presented here in full for the first time.