In this study, we investigate the characteristics of the LIBS plasma in Martian atmospheric conditions using stationary modeling of the LIBS plasma. LIBS spectra are simulated from a one-dimensional model of the plasma divided into two zones along the line of sight. The simulations are based on local thermal equilibrium and carried out using radiative transfer. The simulated spectra are fitted first to synthetic LIBS spectra to test the implementation and in a second step to time-resolved LIBS data of a carbonate sample obtained in experimentally simulated Martian atmospheric conditions. From the fits to the synthetic LIBS spectra, we confirm that plasmas with spatial gradients in the temperature and densities can be well described in a two-zone plasma model. From the fits to the measured data this observation also holds true. We find that the most of the emission lines are well described in the two-zone model and that the two-zone model is a significant improvement from the one-zone model. Furthermore, we obtain typical values of the plasma properties in the two-zone approximation from 500 ns to 1250 ns after plasma initiation and derive the effect of self-absorption, which is predicted to decrease the strongest pixel intensities by a factor of almost two orders of magnitudes.

Chlorine and fluorine play an important role in the geological history of Mars due to their high concentration in Martian magmas and their influence on the generation and evolution of Martian basalts. Chlorine-bearing salts could also facilitate the formation of eutectic brines that could be important for the fluvial history of Mars. The LIBS instruments of ChemCam and SuperCam can detect emission lines of Cl and F, but the intensity of these emission lines is comparatively low, making it difficult to quantify them correctly. A promising alternative is the quantification by molecular emission of diatomic molecules like CaCl and CaF, which can be observed as intense molecular bands in LIBS spectra if Ca is also present. However, the nonlinear dependence of the band intensity on the concentrations of both elements needs to be considered. In this study, we expand upon our previous analysis of molecular bands by investigating samples which produce CaCl bands, CaF bands, or both. We find that the highest CaCl band intensities are found in samples containing more Ca than Cl, while the strongest CaF bands are found in samples with roughly equal concentrations of Ca and F. Both observations can be described by the model that we present here. We also find that the CaCl band is significantly stronger for a sample containing CaCl2 than it is for a sample containing the same concentrations of Ca and Cl in separate bonds. The opposite is true for the CaF band, which is significantly weaker for the sample containing CaF2 bonds than it is for the sample that does not contain CaF2 bonds. These matrix effects are partially attributed to fragmentation during the ablation process and differences in the dissociation energies. Furthermore, we observe that CaF formation is not affected by competing CaCl formation, while CaCl is strongly affected by competing CaF formation. All measurements are done in simulated Martian atmospheric conditions in order to assist the analysis of Martian LIBS data.

By making use of an innovative, low mass, mobile robotic payload following the Lunar Exploration Advisory Group (LEAG) recommendations, many of the international science community’s objectives can be met at lower cost. As a main objective LUVMI was designed specifically for operations at the South Pole of the Moon with a payload accommodated by an innovative lightweight rover with a range of several kilometres. Over the past two years, the key LUVMI scientific instruments – a Volatiles Analyser (VA) and a Volatiles Sampler (VS), were successfully developed and validated (up to TRL 5-6), and new light field cameras were experimented. They were integrated onto a ground prototype of a purposely developed LUVMI rover and tested altogether in a series of outdoor trials, in rocky and sandy environments. Based on these successful results, the recently started LUVMI-X project shall extend the LUVMI rover’s capabilities to enable more comprehensive scientific investigations. Its suite of science instruments will be upgraded and extended, and a flexible and innovative payload infrastructure will create the foundation for commercial payload services.