Volatile loss during heating of lunar mare simulants and related compositions

Due to the scarcity of returned lunar regolith samples, simulants are currently widely used for testing and validation of technologies destined for resource extraction and manipulation on the Moon's surface. Deductions about thermal processing parameters (such as temperature ranges associated with sintering and melting) and material properties rely on a close fidelity of the terrestrially-sourced simulant materials. To evaluate the degassing behaviour of lunar regolith simulants during heating and thereby inform the validity of comparisons to the behaviour expected of actual lunar regolith, we compare profiles via simultaneous differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and evolved gas analysis (EGA) across a range of designated mare simulants, freshly recovered volcanic samples, and synthesised lunar-like glasses. Simulants generally exhibit higher mass loss (related to volatile release at sub-solidus temperatures) than fresh volcanic material, though overlap is observed with one simulant (JSC-1A). Of the fresh sources, Etna ash most closely limits the anticipated water loss difference to original lunar soils to within one order of magnitude. Results from complementary neutron powder diffraction (NPD) indicate that a lowering of the melting onset due to volatile fluxing persists ca. 200–300 °C beyond the major degassing range in samples of several grams. The possibility to reduce the simulant fidelity gap through critical source selection and their inherent limitations are discussed, and refined pre-treatment recommendations are made.