LRO‐LAMP Lunar South Pole Cold Traps: Assessment of H₂O and Potential CO₂ and NH₃ Reserves

Abstract

Nighttime Lyman Alpha Mapping Project (LAMP) observations are used to investigate condensed volatiles at the south polar region of the Moon. This study incorporates LAMP data from the first ∼7 years of the mission and Diviner annual maximum temperatures to search for volatile signatures associated with H2O, NH3, and CO2. Other stable potential species, for example, SO2 and H2S, are not identifiable with the ultraviolet ratio‐temperature techniques and are not directly addressed in this study. We confidently detect a ∼20% increase in normalized Off‐band (175–190 nm) to On‐band (148–162 nm) albedo ratios (consistent with condensed surface volatiles) at temperatures below ∼115 K. Elevated normalized ratios extend to temperatures capable of supporting pure aforementioned ices over geologically long time scales. Although ∼115 K is consistent with H2O lifetimes of ∼1‐Myr, the presence of CO2 and NH3 are not uniquely delineated by the data trends with temperature. Future spectral modeling to appropriately identify the composition and abundance of these condensed volatiles remains necessary. Normalized albedo ratios are further analyzed for candidate species via maximum temperatures to inform the likelihood of ice signatures: H2O (70 K < T ≤ 115 K), NH3 + H2O (60 K < T ≤ 70 K), and CO2 + NH3 + H2O (T ≤ 60 K). We compare normalized albedo ratios across seven regions of interest (ROI), including Faustini, Shoemaker, Haworth, Cabeus, Amundsen, Nobile, and an unnamed region. Such comparisons allow for characterization of relative abundances of volatiles across the ROI important for their utilization in future crewed and robotic missions to the Moon.

Surface Roughness at the Moon’s South Pole: The Influence of Condensed Volatiles on Surface Roughness at the Moon’s South Pole

“…Consistent with previous results, we find decreased roughness values (subdued roughness) at cold-trap temperatures. Further, as shown by Magaña et al (2023), Off-band/On-band ratios are increased at these cold-trap temperatures. Therefore, a trend between surface roughness, Off-band/On-band ratio, temperature, and sublimation rates is evident.…”

“…Minor volatile species such as CO 2 (2wt% relative to H 2 O) and NH 3 (6wt% relative to H 2 O) may contribute to the observed Off-band/On-band ratio; however, delineation from H 2 O is challenging owing to overlapping regions of thermal stability and reduced statistics at CO 2 and NH 3 temperatures. Sine water ice is expected to be the major volatile component, we therefore only consider the H 2 O volatile population (Magaña et al 2023).…”

“…Finally, we compare south pole roughness ratios with LAMP normalized Off-band/On-band ratios (Magaña et al 2023). Normalized Off-band/On-band ratios serve as an indicator for condensed H 2 O within the topmost ∼100 nm.…”

“…We consider 5179 4 km pixels in this analysis. The south pole LAMP data set utilized here is described in Magaña et al (2022), and normalized Off-band/On-band-temperature data and surface sublimation rates are described in Magaña et al (2023). Normalized Off-band/On-band ratios are denoted by colored symbols, where the color scale has a threshold at a minimum of 1.0, indicating ice-free regions; ratios of 1.1 are consistent with ∼0.1 wt.% water ice (Magaña et al 2022).…”

“…Permanently shadowed regions (PSRs) at the lunar poles result from the low obliquity of the Moon's spin axis relative to the ecliptic plane. The lack of solar illumination within PSRs (Mazarico et al 2011) aids in sustaining low temperatures and creates environments known as cold traps capable of retaining condensed volatiles over geologically long time periods (e.g., Schörghofer & Williams 2020;Landis et al 2022;Magaña et al 2023). Condensed volatiles and PSRs are of great interest, both as a scientific record of the volatile history of the Earth-Moon system and for resource utilization.…”