In-situ Detection and Quantitative Analysis Methods for Lunar Water Ice in PSRs

Remote sensing has identified water-ice in the Moon’s polar regions; however, it cannot directly verify the existence and origin of lunar water in the permanently shadowed regions. The LUnar soil Water molecular Analyzer (LUWA) is a key payload on the mini-flying probe of China’s forthcoming Chang’E-7 mission, scheduled for launch in 2026. The mission aims to perform the first in-situ detection of water ice and volatiles of the lunar south pole. LUWA comprises a tunable laser spectrometer (TLS) for in situ analysis of H₂O and HDO, as well as a time-of-flight mass spectrometer (TOF-MS) for the analysis of gas molecules with mass numbers under 200 amu, including H₂O, CO₂ and CH₄. A differential absorption spectrometer (DAS) will be mounted on the leg of the probe to pre-detect the existence of water-ice and monitor its content during drilling. Ground testing demonstrates LUWA’s capability to detect water ice at concentrations as low as 0.01 wt% in evolved gas analysis mode and ≥0.5 wt% through DAS, with water content quantification achievable within the 0.1–4.5 wt% range and δD precision of ±50‰. Key challenges include correcting sublimation losses, adsorption effects, and isotopic fractionation during sample handling. LUWA will provide critical data on the abundance, origin, and distribution of lunar water, supporting future in-situ resource utilization and enhancing our comprehension of volatile dynamics on the Moon.