There is a hole on the Moon, and scientists want to know what’s underneath it.
NASA has selected a project called GIMLI, led by the Planetary Science Institute (PSI) in Tucson, Arizona, to investigate the Marius Hills Pit — an opening in the Moon’s surface that may lead into a large underground lava tube. PSI announced the selection on Oct. 1.
If a cave is there, it could one day help protect astronauts from some of the harshest conditions in the solar system.
What is the Marius Hills Pit?
The pit sits in the Marius Hills, one of the Moon’s most volcanically varied regions. Tech Times reports that the opening is roughly 65 meters (about 210 feet) wide.
Scientists have long suspected that some lunar pits are “skylights” — places where the roof of an old lava tube has collapsed. Lava tubes form when the outer layer of a lava flow cools and hardens while molten rock keeps flowing underneath. When the flow drains away, a tunnel is left behind.
On Earth, lava tubes are usually modest in size. On the Moon, with its weaker gravity, they could be much larger. Tech Times notes that orbital data suggests possible lunar tubes could exceed 1 kilometer (about 0.6 miles) in width and height.
How GIMLI will look underground
You can’t simply peer into a dark hole and map a cave from above. GIMLI will instead combine several ways of “seeing” beneath the surface:
- Ground-penetrating radar, supplied by the Norwegian Space Agency, sends radio waves into the ground and listens for echoes from empty spaces.
- An active seismic system, built by Honeybee Robotics, a Blue Origin company, creates small vibrations and measures how they travel through the rock. Tech Times describes this as the first intentional seismic survey on the lunar surface since Apollo 17 in 1972.
- A gravimeter looks for slight drops in gravity that hint at missing mass — exactly what a large hollow would produce.
- Cameras will photograph the pit and its walls.
“Combining that method with ground-penetrating radar and gravity measurements” will give the team a much better picture of what’s below the surface, said principal investigator Than Putzig, PSI’s associate director, referring to the seismic survey.
The instruments are planned to fly on a lander and rover through NASA’s Commercial Lunar Payload Services program, which pays private companies to deliver science equipment to the Moon. GIMLI was chosen through NASA’s PRISM program, which selects science investigations for those deliveries.
Why a cave would matter
The Moon’s surface is brutal. There is no thick atmosphere or magnetic field to block radiation, small meteorites strike without burning up, and temperatures swing from about minus 280°F (minus 173°C) to about 260°F (127°C).
A lava tube could offer natural shielding from all three without astronauts needing to haul heavy protective materials from Earth. That’s why NASA framed the selection as part of its broader effort to prepare for a long-term human presence on the Moon. Two other investigations were selected at the same time: a station to monitor the environment near the lunar south pole and an instrument to measure ice in permanently shadowed cold traps.
More than a shelter
Even if the cave turns out to be small, the pit is a valuable science site. Its walls expose layers of ancient lava, offering a rare cross-section of the Moon’s volcanic history. The team also wants to learn how the pit itself formed.
Partners on the project include Boise State University, Johns Hopkins University, the Lunar and Planetary Institute and the University of Oslo.
What happens next
For now, GIMLI exists as a plan and a team. Selection allows the project to move into building and testing its instruments. Once a commercial lander is assigned, the team will have a ride to the Marius Hills region.
If the measurements do reveal a large, stable void, the next questions get practical: how big is it, how thick is the roof, and could people or robots safely get inside? Answering those would take further missions. But knowing whether a cave exists at all is the essential first step, and GIMLI is designed to answer exactly that.
The catch
There’s no launch date yet. Selection means hardware development can begin, but the mission still depends on a commercial lander delivering it safely. And until GIMLI takes its measurements, the giant cave remains a strong possibility, not a confirmed fact.
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Sources
- Planetary Science Institute: PSI-led team selected for NASA PRISM program to explore potential lunar cave
- ScienceDaily: This mysterious hole on the Moon may open into a giant cave
- Tech Times: NASA picks lunar lava tube hunt, first surface seismic survey since Apollo
- Space & Defense: NASA selects three new science investigations for Moon Base