Geomorphometric Assessment of the Marius Hill’s Pit for LunarLeaper

LunarLeaper is an ESA Small Mission candidate, aiming to robotically investigate lunar volcanic pits and associated subsurface lava tubes. Lunar pits likely represent collapsed ceilings of lava tubes, providing unique access to the lunar geologic record. One possible landing site for the LunarLeaper mission is the Marius Hills pit (MHP). The MHP is located within a sinuous rille in the region of Oceanus Procellarum (14.1ºN, 303.2ºE). Multiple exposed layers along the pit wall offer a unique opportunity to study the evolution of lunar volcanism, potentially revealing insights into the Moon's geological history. A thorough characterization of the lava tube may also pave the way for future human missions, as underground sites offer natural protection from the Moon's harsh surface conditions.

As part of the mission, the LunarLeaper, a legged robot, will explore the pit using high resolution cameras and possibly spectrometers, taking different images of the wall and the interior of the pit from different locations along the rim. Our main goals are to (1) characterize the slope and trafficability around the rim, (2) use the geomorphometry of the MHP to characterize and quantify viewing conditions, and (3) assess the need for and benefits of a mast-mounted camera. In this study, we use 3D point cloud reconstruction from Lunar Reconnaissance Orbiter Narrow Angle Camera images (Wagner and Robinson, 2022), to perform a geomorphometric assessment of the site. We analyze the slope and trafficability around the pit, which provides essential data in evaluating the robot’s ability to establish a line-of-sight with the pit wall and floor. Next, using ray-casting, we evaluate the overall visibility of the pit walls and floor if observed from the rim, exploring the balance between visibility/science return and the physical stability of the robot. Then, we identify optimal positions along the rim for which LunarLeaper can achieve a maximum level of visibility. In parallel, we evaluate the need for and benefits of a mast-mounted camera to enhance LunarLeaper’s ability to view into the MHP’s deep interior. Finally, we examine trade-offs between the slope angle traversed on the rim and mast height to achieve optimal visibility into the MHP while minimizing mission risk.

Our findings indicate that it is possible to capture depths down to 30 meters and on average 25 meters while remaining on low risk, i.e., less than 15 degree slopes. Additionally, using a relatively short mast (under 1 meter) enables the capture of the pit's deepest regions and the underlying lava tube. The outputs of this study will be used for mission design by providing input on (1) LunarLeaper design trade-offs, e.g., the possible addition of a camera mast, (2) the concept of operations e.g. with respect to path planning, and (3) the optimization of the scientific return of the overall mission.