Picture a pit on the Moon wide enough to swallow a city block, dropping into darkness with no visible floor. That is the Marius Hills Pit, sitting inside one of the most volcanically restless regions of the lunar surface. For years, scientists peering down from orbit have wondered what lies beneath its rim. Now NASA has chosen a mission to go and find out directly, by landing on the Moon and actually shaking it.

The project, called GIMLI, is led by Than Putzig of the Planetary Science Institute, working with Honeybee Robotics and the Norwegian Space Agency. Its method sounds almost old-fashioned: set off small seismic pulses on the surface and listen for how the vibrations bounce back. Apollo astronauts tried something similar decades ago, but, as Putzig put it, "it has essentially not been done since the Apollo astronauts conducted the first seismic surveys on the moon." Paired with ground-penetrating radar and gravity sensors, the technique should let researchers map whatever lies hidden beneath the pit without ever lowering a camera into it.

What they are hoping to confirm is a lava tube, a tunnel-like cavity thought to have formed when molten rock drained out from beneath a hardened crust billions of years ago. If one exists here, it could stretch for a considerable distance away from the pit's opening, offering something the open lunar surface cannot: shelter. Astronauts above ground face radiation exposure and temperature swings of hundreds of degrees between lunar day and night. A buried tube could soften both problems dramatically.

The equipment will travel aboard a commercial lander and rover under NASA's CLPS program, the same scheme ferrying smaller science payloads to the Moon ahead of crewed Artemis missions.