Search

Multiple sets of laser-induced breakdown spectroscopy (LIBS) instruments, including ChemCam (Curiosity), SuperCam (Perseverance), and the Mars Surface Composition Detector (MarSCoDe, Zhurong), are working currently on the surface of Mars, a booming scene of LIBS technology application to planetary exploration. One of the primary challenges faced by those LIBS instruments is accurate and quantitative chemical composition determination of unexplored geological targets. Elastic net is a linear regression model that combines ridge regression and lasso model, which inherits the sparseness of lasso and the stability of ridge. In this work, we investigated the spectral features selected by elastic net model, the model performance and application to over 23,000 LIBS points. Selected features exhibit significant emission lines that are attributed to a certain single element and a few lines attributed to other related elements. These features enhance the interpretability of the model and weaken the matrix effect in LIBS quantitative analysis. In comparison, the results of elastic net are comparable and may be slightly better in some cases than other common linear regression models. For igneous calibration targets (norite, picrite, and shergottite), the predictions of elastic net are closer to the values measured in Earth laboratory than the final multivariate oxide composition values predicted by ChemCam team. Finally, we predicted the oxide abundances of 8 major elements from Mars LIBS spectra of over 23,000 points using elastic net. The predicted values of the elastic net models are highly correlated with those from the ChemCam team model. These results indicate that elastic net is viable for quantitative analysis Mars LIBS spectra. We propose that elastic net is an important candidate model for the quantitative analysis of the Zhurong MarSCoDe LIBS spectra. [Display omitted] • Regression coefficients of elastic net are related to the element LIBS lines. • The errors of major elements were comparable to PLS1-SM results. • Model accuracy was validated by six ChemCam calibration targets. • Chemical components were derived from >23,000 LIBS points. • The Elastic Net models were much more robust to wavelength shifts than the LASSO models. [ABSTRACT FROM AUTHOR]

Numerous occurrences of hydrated minerals (e.g., phyllosilicate, sulfate) have been found on the surface of Mars by remote sensing and in-situ exploration missions, providing strong evidence of the aqueous environment in Martian history. However, the detailed origin of these hydrated minerals is often controversial, reducing their usefulness in constraining the aqueous history of Mars. For instance, in Ophir Chasma, the origins of hydrated sulfates are debatable among hypotheses of precipitating from groundwater, paleolake, or meteoric water. In this study, we performed detailed mineralogy, morphology and stratigraphy analyses of the hydrated phases in the mineral bowl, a depression between the southern wall and mensa of Ophir Chasma, using datasets from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), High Resolution Imaging Science Experiment (HiRISE) and High Resolution Stereo Camera (HRSC). A large number of monohydrate sulfates (MHS), polyhydrated sulfates (PHS) and some jarosite were identified in this region. Elevation of PHS-rich regions (mean elevation of −1130 ​m) is higher than those of MHS (mean value of −1401 ​m). Spectra of poly- and monohydrated sulfates mixtures were investigated in details in laboratory. Spectral features (i.e., band depth of ~1.9 ​μm, 2.1 ​μm, convexity at 2.1 ​μm and 2.4 ​μm) of sulfates mixtures changed regularly with the abundance of endmember. The linear function between the ratio of BD2100_2 to SINDEX2 and kieserite component was set up to estimate hydrated sulfates abundance. We employ the function onto CRISM data and find a coexistence of poly- and monohydrated sulfates for the formerly recognized PHS endmember, which may indicate a local dehydration/rehydration process for the sulfated minerals. Comprehensive mineralogy, topography, and stratigraphy analyses of hydrated sulfates outcrops suggest a complex formation scenario which could include surface runoff, paleolake, even aeolian erosion. • Spectral features at ~2 ​μm derived from laboratory sulfates mixtures changed regularly with the abundance of endmembers. • We calculated the abundance of hydrated sulfates in Ophir Chasma using CRISM spectral dataset. • Alternative formation scenarios of sulfates in the mineral bowl of Ophir Chasma were detailed discuss. [ABSTRACT FROM AUTHOR]

China's first Mars exploration mission, named Tianwen-1, landed on Mars on 15 May 2021. The Mars Surface Composition Detector (MarSCoDe) payload onboard the Zhurong rover applied the laser-induced breakdown spectroscopy (LIBS) technique to acquire chemical compositions of Martian rocks and soils. The quantitative interpretation of MarSCoDe-LIBS spectra needs to establish a LIBS spectral database that requires plenty of terrestrial geological standards. In this work, we selected 316 terrestrial standards including igneous rocks, sedimentary rocks, metamorphic rocks, and ores, whose chemical compositions, rock types, and chemical weathering characteristics were comparable to those of Martian materials from previous orbital and in situ detections. These rocks were crushed, ground, and sieved into powders less than <38 μm and pressed into pellets to minimize heterogeneity at the scale of laser spot. The chemical compositions of these standards were independently measured by X-ray fluorescence (XRF). Subsequently, the LIBS spectra of MAL standards were acquired using an established LIBS system at Shandong University (SDU-LIBS). In order to evaluate the performance of these standards in LIBS spectral interpretation, we established multivariate models using partial least squares (PLS) and least absolute shrinkage and selection (LASSO) algorithms to predict the abundance of major elements based on SDU-LIBS spectra. The root mean squared error (RMSE) values of these models are comparable to those of the published models for MarSCoDe, ChemCam, and SuperCam, suggesting these PLS and LASSO models work well. From our research, we can conclude that these 316 MAL targets are good candidates to acquire geochemistry information based on the LIBS technique. These targets could be regarded as geological standards to build a LIBS database using a prototype of MarSCoDe in the near future, which is critical to obtain accurate chemical compositions of Martian rocks and soils based on MarSCoDe-LIBS spectral data. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is a valuable tool for evaluating the geochemical characteristics of Martian rocks and was applied in the Tianwen-1 Mars exploration mission with the payload called Mars Surface Composition Detection Package (MarSCoDe). In this work, we developed a laboratory standoff LIBS system combined with a Martian simulation chamber to examine the geochemical characteristics of igneous rocks, with the intention to provide a reference and a basis for the analysis of LIBS data acquired by MarSCoDe. Fifteen igneous geological standards are selected for a preliminary LIBS spectroscopic study. Three multivariate analysis methods were applied to characterize the geochemical features of igneous standards. First, quantitative analysis was done with Partial Least Squares (PLS) and Least Absolute Shrinkage and Selection (LASSO), where the major element compositions of these samples (SiO2, Al2O3, T Fe2O3, MgO, CaO, K2O, Na2O, and TiO2) were derived. The predicted concentrations ((Fe2O3 + MgO)/SiO2, Fe2O3/MgO, Al2O3/SiO2, and (Na2O + K2O)/Al2O3) were used to identify the geochemical characteristics of igneous rocks. Also, PCA, an unsupervised multivariate method was tested to directly identify the igneous rock lithology with no prior quantification. Higher correlation (0.82–0.88) are obtained using Principal Component Analysis (PCA) scores than using predicted elemental ratios derived by PLS and LASSO, indicating that PCA is better suited to identify igneous rock lithology than via quantitative concentrations. This preliminary study, using this LIBS system, provides suitable methods for the elemental prediction and geochemical identification of martian rocks, and we will use extended geologic standards and continue to build a robust LIBS spectral library for MarSCoDe based on this LIBS system in the future. [ABSTRACT FROM AUTHOR]