Laser-induced Breakdown Spectroscopy of Ice-regolith Mixtures: Implications for Measurements on Planetary Surfaces

Abstract Laser-induced breakdown spectroscopy (LIBS) is an analytical technique enabling in situ chemical analysis of planetary surfaces. Its use on the Mars Science Laboratory and Mars 2020 missions has demonstrated the potential for quantifying water in hydrated minerals, prompting investigations into its application for detecting and quantifying water ice in lunar regolith. Although promising results have been reported under vacuum conditions, previous measurements do not fully represent the range of physical forms that ice-regolith mixtures may take on the Moon. In this study, we use a scanning LIBS micro-analyzer to assess the main sources of signal variance and the response of the H α emission line to 0–40 wt% water ice in two types of ice-regolith mixtures. We find that the primary factor influencing hydrogen emission is enhanced laser coupling with larger grains in wet or ice-cemented regolith due to increased cohesion. Emission from “cemented” ice-regolith mixtures exhibits increasing H α intensity up to ∼15 wt%, followed by a decline attributed to water saturation. In contrast, emission from “discrete” ice-regolith mixtures shows no consistent H α response in the 0–10 wt% range. Regression models trained on physically diverse mixtures reduce the rms error of predicted H 2 O content by 5.6% across the 0–40 wt% range. These results highlight the need for calibration using geologic materials that reflect grain size, porosity, and type of ice-regolith mixture. They also demonstrate the value of scanning LIBS technologies for identifying sources of signal variability in planetary applications.