Multispectral and Morphological Study of a Lunar Far Side Crater in the South Pole–Aitken Basin

The South Pole–Aitken (SPA) basin is the largest and deepest impact structure on the Moon’s far side and the largest known impact crater in the Solar System. This region is of significant scientific interest due to its distinctive morphological, optical, and thermal characteristics, which suggest the possible presence of water ice in permanently shadowed regions (PSRs).

Within the SPA basin lies a zone containing five impact craters named in honor of the renowned Colombian astronomer Julio Garavito Armero. This study presents a detailed multispectral and morphological analysis of this specific area, using datasets from several missions, including NASA’s Lunar Reconnaissance Orbiter (LRO), the China National Space Administration’s Chang’e program, and India’s Chandrayaan mission from ISRO.

For the morphological analysis, we processed digital elevation models (DEMs) from different sources to characterize the region’s principal geomorphological features. These include estimates of crater floor diameters—up to approximately 80 km in the largest crater—and elevation variations ranging from –5000 m to –500 m. We inferred aspects of the impact events that shaped the main depressions, identified dominant landforms such as ridges, grabens, and possible mare-like structures, and performed a slope distribution analysis to assess crater wall morphology. Additionally, using geological composition data, we estimated the age and origin of the craters, suggesting formation during the Nectarian to Imbrian periods. These features help constrain the composition and mechanical behavior of the local regolith.

For the multispectral analysis, we examined visible and thermal infrared emissions, as lunar surface radiation comprises both reflected sunlight and emitted thermal energy. Using data from the Moon Mineralogy Mapper (M3) aboard Chandrayaan-1, we analyzed reflectance as a function of radiance (I), solar flux (F), and the Sun-Moon distance (d), following radiative equilibrium principles.This relationship is expressed by the equation:​

where IoF represents the apparent reflectance, allowing us to derive the spectral behavior of the surface independent of solar distance and illumination conditions.

We derived surface albedo at 750 nm and identified key absorption features associated with olivine and pyroxene. To estimate surface temperatures, we applied thermal correction techniques based on the methodology proposed by Clark et al. (2011).

We then integrated all datasets to evaluate how morphological features influence local solar illumination and thermal conditions. Variations in surface slope and orientation significantly affect apparent reflectance (I/F) and emissivity values, leading to deviations in the inferred thermal component. Sun-facing slopes tend to exhibit higher I/F values and lower apparent thermal emissions, while slopes facing away from the Sun appear cooler with reduced reflectance but artificially high thermal signals. In our estimations, the most exposed surfaces reached temperatures of up to 420 K. Overall, the interplay between morphology, optical properties, and thermal behavior governs the physical state of the regolith, influencing its composition, structure, and potential for volatile retention.

These findings enhance our understanding of the geological and thermal dynamics of the lunar far side and offer valuable insights for future landing site selection and exploration strategies in the SPA region.