This mysterious hole on the Moon may open into a giant cave

The project will receive funding through NASA's Payloads and Research Investigations on the Surface of the Moon (PRISM) program. PRISM sends scientific instruments to the lunar surface aboard spacecraft supplied by providers participating in the Commercial Lunar Payloads Services (CLPS) initiative.

GIMLI Will Probe Beneath the Moon

The selected project, known as the Geophysical Instruments for Marius Lunar pit Investigation, or GIMLI, is led by PSI Associate Director and Senior Scientist Than Putzig. PSI is working with Honeybee Robotics, which will construct much of the mission's equipment and instrumentation. The instruments will travel aboard a lander and rover supplied through the CLPS initiative. PSI's work will also be conducted in partnership with the Norwegian Space Agency.

"GIMLI represents the type of ambitious planetary science that PSI was built to pursue," said PSI Director and CEO Amanda Hendrix. "Than and his team are taking a scientific question we've been studying from orbit and have developed a way to investigate it directly on the Moon. We're excited to have PSI leading this effort and to be partnering with NASA and Honeybee Robotics to learn more about the Moon and its volcanic past."

Scientists studying the Moon from orbit have found compelling evidence that caves and lava tubes could be hidden beneath its surface. GIMLI will concentrate on the Marius Hill Pit (MHP), a large opening located within one of the Moon's most volcanically varied regions. Like other pits identified on the Moon, MHP could provide an entrance into underground structures created by ancient volcanic activity.

Rather than relying only on observations from above, GIMLI will give researchers an opportunity to examine MHP directly from the lunar surface.

Radar and Seismic Sensors Will Search for a Lava Tube

"It's long been a desire of mine to reintroduce intentional active-source seismic methods to planetary science, as it has essentially not been done since the Apollo astronauts conducted the first seismic surveys on the Moon," shared Putzig. "Combining that method with ground-penetrating radar and gravity measurements makes it all the more exciting, as these methods together will allow us to get a much better understanding of subsurface properties -- including the anticipated detection of a lava tube extending away from the Marius Hills pit."

To investigate what lies underground, GIMLI will combine ground penetrating radar, seismic sensors, and a gravimeter. Cameras will also photograph the lunar surface and the exposed walls of the pit. Used together, these instruments will search for a possible underground void extending from MHP and, if one is detected, help scientists estimate its dimensions.

Honeybee Robotics, a Blue Origin company, will be PSI's commercial partner on the project. The company will provide project management services and construct instrumentation for the active source seismic system, the gravimeter, and the cameras. Honeybee Robotics will also help integrate the scientific instruments onto the lander and rover. Along with PSI, it will lead instrument operations after the spacecraft reaches the lunar surface.

Even No Cave Would Reveal New Lunar Geology

The mission could still produce important discoveries even if researchers find no cave or lava tube. Its measurements could help address another major question: How did the Marius Hill Pit form?

By examining the material surrounding and beneath MHP, scientists could gain new clues about the pit's origin as well as the geology and volcanic history of the wider region.

The team also plans to study more than the possible underground structure. The surrounding area has experienced a long history of volcanic activity, and the walls of MHP expose layers of regolith and lava flows that normally remain buried. Examining these layers could show how lava once moved across and beneath the lunar landscape and whether individual eruptions were separated by long intervals.

Lunar pits are valuable not only because their walls expose otherwise hidden geology. Any underground spaces connected to them could also preserve evidence of the volcanic processes that helped shape the Moon.

A Window Into the Moon's Volcanic Past

"Confirming a substantial lava tube would give us an insight into how volcanism operated on the Moon," explained Gareth Morgan, PSI Senior Scientist and Deputy Principal Investigator on the GIMLI program. "Lava tubes are a common feature of basaltic volcanism on Earth, so identifying them on the Moon means we could use knowledge of such terrestrial caves to better understand lunar history."

In addition to PSI and Honeybee Robotics, the GIMLI team includes Co-Investigators from Boise State University, Johns Hopkins University, the Lunar and Planetary Institute, and the University of Oslo. The Norwegian Space Agency will provide the ground-penetrating radar.