Morphometric Analysis of Lunar Pits and Robotic Mission Design for In-Situ Exploration

MORPHOMETRIC ANALYSIS OF LUNAR PITS AND ROBOTIC MISSION DESIGN FOR IN SITU EXPLORATION. Demur Merkviladze1, Matteo Massironi2,3 , Riccardo Pozzobon2,4 , and Francesco Sauro2 , 1 Department of Earth and Planetary Sciences, University of Nantes, France, 2 Department of Geosciences, University of Padova, Italy, 3 Center of Studies and Activities for Space “G. Colombo”, University of Padova, Italy 4 Dipartimento di Fisica e Astronomia "Galileo Galilei", Università degli studi di Padova, Italy Contact e-mail: [email protected] Introduction: In past decades, the surface of the Moon has been extensively explored; however, the subsurface of our satellite remains hidden from the human eye. Lunar pits represent windows to underground voids and thus appear as targets for further research. The great majority (250 out of 279!) of these features are identified as impact melt pits, however, are often overlooked and attract much less attention than their mare counterparts. In this study, we conduct a geomorphological analysis of impact melt pits to better understand their formation, morphology, and potential scientific value. Furthermore, we propose a mission concept focused on in situ exploration of selected impact melt pits, outlining instrumentation, landing strategies, and mobility solutions to maximize scientific return. This research aims to bridge the knowledge gap surrounding impact melt pits and highlight their importance for future lunar exploration and habitation prospects. Methodology: LROC NAC images of 202 pits - comprising those from 10 impact melt ponds and mare pits - were obtained and processed using the USGS PILOT website [1]. The inner diameters of those pits were mapped in QGIS, based on the Lunar Pit Catalogue [2]. A range of morphological parameters was extracted and computed, including major and minor axes, area, perimeter, depth, aspect ratio, asymmetry ratio, and irregularity index. To facilitate analysis, the pits were categorised into three morphological classes: collapse, fracture, and dome (Fig. 1). The compiled dataset, stored as a CSV file, was processed and visualized using Python, enabling statistical comparisons and graphical representations of the observed trends. Results and discussion: The morphological analysis reveals significant differences between mare pits and impact melt pits in terms of size, shape, and structural complexity: • Mare pits are generally larger and deeper than impact melt pits (Fig. 2a), indicating a different formation process and greater subsurface void development. • They exhibit a lower aspect ratio and a smaller irregularity index (Fig. 2b), meaning they are more circular and geometrically regular compared to impact melt pits. • Impact melt pits, in contrast, display greater variability in shape and asymmetry, suggesting that they are influenced by heterogeneous structural adjustments in the melt deposits. The classification of impact melt pits into collapse, fracture, and dome-related pits suggests that they originate from different geological processes: • Collapse Pits: Likely formed due to subsurface voids created as impact melt cools and contracts. The overlying material loses support and collapses into the cavity. • Fracture-Related Pits: These pits are often elongated or clustered along linear features, suggesting a formation mechanism linked to tensile stress in cooling melt surfaces. Over time, the crust experiences extension and separation, creating elongated depressions that may later evolve into larger pits. • Dome-Associated Pits: These pits are often found atop small extrusive features, indicating that gas release during impact melt cooling may have played a role in their formation. The trapped volatiles escape to the surface, forming a raised dome with a central pit, resembling extrusive volcanic vents. Fig. 2: Scatter plots comparing the morphological characteristics of lunar pits. The left panel shows the relationship between perimeter and depth, while the right panel illustrates the correlation between irregularity index and asymmetry ratio, with Impact Melt and Mare pits distinguished by color and marker. Fig. 1: Example of mapped pits and their assigned classes: a) Copernicus 20 – fracture; b) Stevinus 25 – collapse; c) King 19 – dome. Mission concept and exploration plan: Among the surveyed melt ponds, King Melt Pond stands out due to its diverse pit morphologies: • It hosts all three pit types (collapse, fracture, and dome-related), making it an ideal site to study the range of impact melt pit formation processes. • Unlike other impact melt ponds, King Melt Pond is located outside its parent crater, presenting a unique opportunity to investigate how impact melt deposits behave beyond the crater boundary [3]. • This site benefits from high-resolution LROC NAC imagery and NAC digital terrain models (DTMs), which provide crucial topographic and structural data for mission planning. Given its scientific significance and favourable data coverage, King Melt Pond has been identified as a prime candidate for a robotic mission dedicated to the in situ exploration of impact melt pits. A planned landing site and exploration path have been proposed to maximize the study of key pit features and gain deeper insights into their formation mechanisms. A systematic, data-driven approach was employed to identify an optimal landing site, prioritizing gentle slopes to ensure a safe descent. This process identified two candidate sites on the eastern plateau—a region with relatively smooth terrain and proximity to high-priority pits (Fig. 3). Post-landing, the rover will conduct a structured traverse to systematically investigate key pits, prioritizing those with distinct morphologies and accessible entry points. For this purpose, two potential traverse routes have been outlined (Fig. 3). Suggested payload for the rover: Stereo Camera; LiDAR; Multispectral camera; GPR; Neutron/Mass Spectrometer; Temperature and Radiation sensors. Conclusion and future work: This morphological analysis underscores the distinct characteristics of lunar impact melt pits compared to their mare counterparts, and provides unique insights into impact melt cooling processes and heterogeneous formation mechanisms. Lunar pits offer potential access points to subsurface environments and may provide sheltered locations for future human habitats [4]. Future work will focus on more detailed analysis and modeling of impact melt pit formation mechanisms, informed by our morphological classifications. Development of the proposed robotic mission to King Melt Pond will continue. In situ exploration will provide crucial ground truth data to validate our findings and further assess the scientific and resource potential of these overlooked lunar features. References: [1] Robinson, M.S., et. al. (2010). Lunar Reconnaissance Orbiter Camera (LROC) Instrument Overview, Space Science Reviews, Vol 150, pp. 81-124. [2] Wagner, R. V. and Robinson, M. S. (2021). Occurrence and Origin of Lunar Pits: Observations from a New Catalog. 52nd Lunar and Planetary Science Conference, Abstract #2530. [3] Ashley, J. W., Robinson, M. S., Hawke, B. R., van der Bogert, C. H., Hiesinger, H., Sato, H., et al. (2012). Geology of the King crater region: New insights into impact melt dynamics on the Moon. Journal of Geophysical Research, 117(E12). [4] J. Blamont, A roadmap to cave dwelling on the Moon and Mars, Advances in Space Research, 54 (2014) 2140-2149. Fig. 3: The map of 2 proposed landing ellipses with suggested traverses and stops for impact melt pit exploration in King Y melt pond.