Stability Assessment of Mare Tranquillitatis Pit's Slopes

STABILITY ASSESSMENT OF MARE TRANQUILLITATIS PIT’S SLOPES. A. Alajrami¹, M. Chwała2 and K. Górniak3, ¹Department of Geotechnology, Hydro Technology, and Underground and Hydro Engineering, Faculty of Civil Engineering, Wrocław University of Science and Technology (abd[email protected].pl), 2Department of Geotechnology, Hydro Technology, and Underground and Hydro Engineering, Faculty of Civil Engineering, Wrocław University of Science and Technology (marcin[email protected]l), 3Faculty of Civil Engineering, Wrocław University of Science and Technology (2713[email protected].edu.pl). Introduction: Lunar lava tube skylights, such as the Mare Tranquillitatis Pit [1], may provide valuable insights into the structural integrity and stability of subsurface voids on the Moon [2]. In particular, understanding stability of their slopes is relevant from the perspective of studying these objects, where approaching the edge of the collapse appears to be the feasible way to examine them [3]. This study proposes a numerical approach to evaluate the slope stability of the Mare Tranquillitatis Pit. A series of cross-sections were extracted from 3D point cloud data [4] and analyzed using computational tools to assess slope failure mechanisms. By implementing Finite Element Limit Analysis (FELA) within Optum G2, collapse multipliers were computed to estimate stability across various scenarios. Key factors such as displacement patterns and energy dissipation were examined to identify potential failure modes [2]. The results provide insights into the structural behavior of the pit edges, highlighting variations in stability across different cross-sections and boundary conditions. These findings contribute to a better understanding of potential slope failure mechanisms in the vicinity of lunar skylights. Summary of Methods: A MATLAB function was created to import and process the OBJ file, which contains the 3D point cloud data [4]. This function reads the file and extracts the X, Y, and Z coordinates of the points, storing them in a matrix for further use. To focus the analysis on the relevant regions of the 3D structure, a filtering process was applied to isolate points within a specified Zcoordinate range. This range was selected to encompass the funnel structure, including both the inner and outer regions and the inner wall of the pit. The analyses were performed in axi-symmetry, where five scenarios were assumed. Each scenario considers a different distribution of surface regolith parameters or assumes them as constant values, along with different topography of the boundary between the regolith and rock. Finite Element Limit Analysis (FELA) method have been implemented by using Optum G2 software to assist the stability of the extracted crosssection of the Mare Tranquillitatis Pit where collapse multipliers for upper and lower boundary were computed to assess failure mechanisms and visualization of displacement and dissipation energy [2]. Figure 1. Collapsing part (red colour) of exemplary Mare Tranquillitatis Pit slope. The axi-symmetry axis is shown as green dased line. Results & Summary: The analysis revealed that certain cross-sections consistently exhibited high stability across all scenarios, while others demonstrated notably lower stability. Additionally, some cross-sections displayed varying stability depending on the scenario. The collapse region was generally observed to follow a funnel-like pattern, influenced by the underlying slope geometry and boundary conditions. A detailed paper on thia subjets will be submitted by the authors in the coming weeks to an appropriate journal. The proposed procedure allows for the assessment of which locations are the safest in terms of slope stability and which are particularly hazardous. Thus, it can be used as a method for designing missions aiming to reach areas near the edges of large lunar collapse pits. Acknowledgments: The work was performed based the research project no. 2023/51/D/ST10/01956, financed by the National Science Center, Poland. References: [1] Sauro, F., Pozzobon, R., Massironi, M., De Berardinis, P., Santagata, T., & De Waele, J. (2020). Earth-Science Reviews, 209, 103288. [2] M. Chwała , G. Komatsu, and J. Haruyama, (2024). Icarus, 411, 115928. [3] Mittelholz et al. (2025). In: 56th Lunar and Planetary Science Conference, #1957. [4] Shea E. K., Wagner R. V., and Robinson M. S. (2022) JGR Planets, 127, e2022JE007328. [5] Carrier W. D., Olhoeft G. R., and Mendell W. (1991) Lunar Sourcebook: A User’s Guide to the Moon, Chapter 9, 475–594.