Summary
NASA selected the Planetary Science Institute-led GIMLI project to investigate whether a large underground void extends from the Moon’s Marius Hills Pit. The planned lander-and-rover study will combine radar, seismic and gravity measurements.
NASA has selected the Planetary Science Institute-led Geophysical Instruments for Marius Lunar pit Investigation (GIMLI) for its Payloads and Research Investigations on the Surface of the Moon (PRISM) program. Announced by PSI on October 1, 2026, the project is designed to investigate whether an underground cave or lava tube extends from the Marius Hills Pit (MHP).
The pit is in one of the Moon’s volcanically diverse regions. Orbital observations have provided evidence that underground caves and lava tubes may exist on the Moon, but GIMLI is intended to investigate MHP directly from the surface. The project will travel on a lander and rover provided through NASA’s Commercial Lunar Payload Services (CLPS) initiative; the announcement does not give a mission date.
Instruments to probe beneath the pit
GIMLI will combine ground-penetrating radar, seismic sensors and a gravimeter, alongside cameras that will image the surface and pit walls. The methods can provide complementary views of the subsurface: radar detects reflections from underground boundaries, seismic measurements record how waves travel through and reflect from material, and gravity measurements can help reveal variations in the distribution of mass. Together, the instruments are intended to search for a void and, if one is present, help determine its size.
The project’s lead, PSI Associate Director and Senior Scientist Than Putzig, described active-source seismic measurements—where a signal is deliberately generated and its response measured—as a central part of the investigation. PSI says that combining this approach with radar and gravity measurements will allow researchers to study subsurface properties at the site.
PSI is partnering with Honeybee Robotics, which will build instrumentation for the active-source seismic system, gravimeter and cameras, and help integrate the instruments onto the lander and rover. The Norwegian Space Agency is providing the ground-penetrating radar. The team also includes researchers from Boise State University, Johns Hopkins University, the Lunar and Planetary Institute and the University of Oslo.
A possible cave and a record of lunar volcanism
A substantial lava tube could help scientists understand how volcanism operated on the Moon. On Earth, lava tubes are common in basaltic volcanic settings; comparing them with lunar structures could provide context for interpreting the Moon’s volcanic history. The pit walls also expose layers of regolith and lava flows that are usually underground. Studying those layers could offer evidence about how lava moved and whether long intervals separated eruptions.
The possibility of a large underground space has a potential future relevance as well: such a cave might offer astronauts shelter from radiation and the Moon’s extreme surface temperature swings. That prospect depends on whether a suitable structure exists. GIMLI’s immediate purpose is to examine the pit and its geology, including the possibility of an underground void.