Moon Diver is a proposed lunar mission concept by NASA's Jet Propulsion Laboratory that would employ a robotic lander and a – distant coaxial – two-wheeled rover called Axel to investigate the exposed geological layers on the walls of a deep lunar pit.

[1][5] The mission concept aims to understand the formation and evolution of the Moon's secondary lava crust by exploring the vertical walls of a pit in Mare Tranquillitatis.

[3] By studying lunar lava, planetary scientists can work out whether the volcanic activity was robust enough to give the moon a Mars-like atmosphere in the distant past.

[7] The mission's lander would feature a highly accurate landing system,[2] allowing the deployment of the rover a few hundred feet from the pit.

[2] The science goals are:[2] Scientists are also interested in lunar lava tubes and caverns because they could provide shelter for future equipment or even crewed research centers.