Mechanochemical Alteration of the Mineralogical Structure and Chemical Composition of Lunar and Martian Analogues

The chemical and mineralogical composition of the Lunar and Martian surface, for instance the presence of inorganics (SiO2, TiO2, CaO, MgO, Na2O, Al2O3 and Fe2O3), water ice (within Lunar cold traps and Martian polar regions) and trace organic compounds (e.g. chlorinated hydrocarbons within Gale Crater on Mars), has been previously studied in detail. However, the specific chemical changes occurring within regolith due to wind-driven and impact processes has only recently been explored. The research presented in this thesis illustrates the novel use of the planetary analogues JSC-Lunar, LHS-1, JSC-Martian and MGS-1 to assess mechanochemical-induced alterations in their chemistry, physical and mineralogical properties through ball milling techniques. This research sought to utilise ball milling techniques upon the named simulants to simulate potential chemical changes due to the collisional impact processing during regolith transport occurring on the Moon and Mars.

Milling experiments within the laboratory have been complemented with a variety of analytical techniques, namely XRD to analyse potential mechanochemical-induced modifications in mineralogy, ATR-FTIR to assess induced chemistry, TGA to observe thermal activation effects and loss of volatiles, and SEM to record alterations in physical properties such as grain size distribution, surface texture and grain morphology. Water ice was also incorporated into milling experiments, and subsequent analogous analyses conducted to assess the effects of collisional processes on regolith-ice mixtures and water ice-driven reactions on the Lunar and Martian surfaces. However, such reactions were more probably driven by water in its liquid state due to a combination of partial melting during the crushing of ice prior to milling and slight increases in temperature within the internal reaction system during the grinding process.

The results in this thesis indicate significant mechanochemical-induced alterations in the properties of planetary analogues, and an increase in mineral surface reactivity. XRD results showed noticeable modifications in relative peak intensities and potentially indicate corresponding mineralogical variations. ATR-FTIR spectroscopy displayed consistent increases in absorbance for the Si-O-M+ (M+ = metal cation) vibrational band after milling. These findings are invaluable when considering the effect of collisional impact processes on planetary surfaces and the transport of their regolith, for instance the dehydroxylation of mechanically activated mineral surfaces through meteoritic impacts on the Lunar surface resulting in H2O2 production, as indicated by toxic moon dust. TGA results in conjunction with infrared spectroscopy have shown the CO2 sequestration ability of the planetary analogues, which is of great significance to the Martian atmosphere and uptake of CO2. The potential formation of hydrated minerals (for instance hydrated silicates) due to water ice experiments, has been suggested through XRD and infrared spectroscopy, which is of relevance when considering areas on the Lunar and Martian surface which contain water ice, or studying the historical hydrological cycle on Mars. Milling experiments also displayed considerable abrasion-induced alterations in physical properties, for instance agglomeration of grains observed for the LHS-1 and MGS-1 simulants indicating potential triboelectrification. This is of high relevance to the future exploration and exploitation of the Lunar and Martian surfaces, due to granular electrification observed through environmental processes such as sandstorms, meteoritic bombardment (and thus regolith transport) and UV irradiation. The experimental analyses of planetary analogues on Earth will assist not only understanding of the Lunar and Martian surface and its regolith composition, but also the manner in which it evolves over time due to environmental processes, thus complementing interpretation from current and future space missions.