UV excited mineral fluorescence observations allow for a potential low-complexity, low-cost method for identifying regions of interest during Martian in-situ observations. However, the effect of low temperature conditions analogues to Martian night-time conditions on fluorescence and phosphorescence behaviour has not been previously researched for minerals relevant for Mars science objectives. Additionally, previous Mars fluorescence observations have mainly used long-wave UV excitation. This research investigates how UV-induced visible mineral fluorescence and phosphorescence signal of Mars relevant minerals are affected by temperatures analogous to Martian night-time conditions, and how these responses may be characterised using an RGB camera-based optical system.

A selected set of Mars-relevant and fluorescent mineral specimens was observed under short-, medium- and long-wave UV excitations (UV275, UV310 and UV365, respectively) using a MAHLI analogue optical system. Observations were acquired at room temperature and at low-temperature conditions using a liquid-nitrogen cooled experimental set-up. The fluorescence response was characterised in terms of detectability, camera specific radiance and chromaticity, and phosphorescence behaviour. As the camera-based RGB data represent integrated CMOS detector responses, the measurements were interpreted as calibrated camera responses.

The results indicate that the excitation wavelength strongly affects fluorescence detectability. Several mineral components were visible under multiple UV wavelengths, whereas others were only detected under specific excitation conditions. Therefore, multi-wavelength UV excitation provides additional information compared to a single long-wave UV observation. Cooling generally increased sustained fluorescence radiance in the robust dataset, although mineral-, activator- and wavelength-dependent exceptions remained prominent. Lowering the temperature of minerals to Martian night-time temperature conditions affected chromaticity data in selected specimens, but most chromaticity shifts remained within the same broad visible colour class and no systematic chromaticity-shift direction was observed across the complete dataset. Phosphorescence showed a stronger dependence on mineral component and temperature: observations at low temperature conditions increased the detectability, initial post-excitation radiance signal or visually determined duration of phosphorescence for several specimens.

The results indicate that RGB UV fluorescence imaging using an enhanced MAHLI analogue can increase the detectability of selected fluorescent and phosphorescent mineral components under Martian night-time analogue conditions using short-, middle- and long wave excitation sources. However, the method is not suitable for definitive mineral, activator or defect identification without spectrally resolved follow-up measurements. Its strongest application is therefore an in-situ triage method for identifying spatially resolved fluorescent regions of interest on the Martian surface that may subsequently be selected for more detailed and costly spectroscopic or geochemical analysis. ... Read more