Lunar Pit Morphology: Implications for Exploration

Lunar pits are small (similar to 10-300 m wide) collapse features with vertical walls and sometimes overhangs. We have identified almost 300 pits, mostly in ponds of cooled impact melt inside large craters younger than similar to 1 billion years. Several of these pits may provide access to lava tubes or other caves, and those in the maria expose the layering record of the top 20-100 m of basaltic lava flows. We investigated the 21 known pits outside of impact melt ponds to determine possible origins, ages, and present-day access to the lunar subsurface. We used Lunar Reconnaissance Orbiter Narrow Angle Camera images (<2 m per pixel) to produce detailed 3D reconstructions of six pit interiors. We evaluated the general morphology and geologic context of all twenty-one. While four pits have contexts suggestive of lava tubes, the majority are ambiguous, although all occur in or near the maria. We also propose that pit formation is an ongoing process, as the degree of degradation of a pit is unrelated to the age of the host terrain. Much of the original volume of most pits is now filled with debris, but some exhibit significant overhangs and may have present-day cave access. Viewing pit walls and floors, even from the rims, requires navigating steep slopes of loose material. Since the floors are also covered with rough debris piles, we recommend simple flying vehicles for initial reconnaissance.