Lunar geochemistry and prospecting with the KPLO Gamma-Ray Spectrometer

We will re-visit the Moon using data acquired by the Korea Pathfinder Lunar Orbiter (KPLO) Gamma Ray Spectrometer (GRS) to better characterize subsurface geochemistry as well as identify and assess potentially useful minerals for in situ resource utilization, paving the way for future human and robotic exploration.

The Moon is a convenient laboratory for understanding processes underlying planetary formation and evolution. The surface of the Moon preserves a record of geochemical processes that occurred primarily during the past 3-4 billion years. Several countries are proposing landed lunar missions, leveraging recent advances in space technology. In addition, evidence for ice in permanently shadowed craters has led to interest in using the Moon as a re-fueling base for human exploration of the solar system.

The elemental composition of the lunar surface provides crucial information needed to understand lunar formation and evolution as well as to identify and extract resources. South Korea’s KPLO employs a GRS to determine subsurface elemental composition. This data set will complement prior missions like Lunar Prospector (LP), Kaguya, and Chang’e that have globally mapped major rock-forming elements, radioelements, and H.

We will fully utilize KPLO GRS’s unique energy range (30 keV-10 MeV) to maximize the scientific return from its data. Specific aims include:
1) Characterize transport and dispersion of volatiles by measuring temporal changes in gamma ray intensities from radon daughter products;
2) Determine the distribution of rare earth elements (REE) within the Procellarum-KREEP Terrane by directly identifying Sm and Gd;
3) Search for hydrogen at poles using the shield detector, providing it is capable of measuring neutrons; and
4) Characterize the distribution of ilmenite in search of 3He with improved mapping of Fe and Ti.

Once we successfully obtain elemental maps, we will cross-validate with elemental datasets reported by prior missions like LP and
Kaguya.

The KPLO GRS utilizes LaBr3, which has significant self-activity due to radiolanthanum, interfering with measurements in the 0.5-3 MeV energy range. This region of the spectrum contains key elemental signatures. We have unique capabilities and experience for data reduction, analysis and modeling, developed during LP, Kaguya, and Dawn missions, which will be needed to remove this contamination for accurate elemental measurements. We will also apply proven peak identification and spectrum analysis methods to the spectral region of 30-200 keV, which has not previously been measured. For example, we will search for 46.5 keV gamma rays from Pb-210, a decay product of volatile Rn-222. Using these methods, it may be possible to determine the concentration of radioelements and REE from its unique energy range, even though the KPLO GRS is not expected to resolve individual peaks.

We will help the GRS team archive the spectra and maps at NASA’s and/or KARI’s Planetary Data System, ensuring the data are promptly available to the lunar community for scientific research and planning.