Beneath the Moon’s battered surface, an enormous underground landscape may be waiting to be explored. Scientists have spent years studying mysterious pits visible in lunar photographs, and a new NASA-supported investigation could help reveal whether one of these openings leads into a much larger hidden cave.
The development, reported in October 2026, focuses on the Marius Hills Pit, a deep opening in an ancient volcanic region of the Moon. Researchers want to determine whether a lava tube extends beneath the opening and how large any underground void might be.
The discovery is intriguing because the Moon is often imagined as an open, lifeless landscape of craters, dust and exposed rock. Yet its geological history may have created enormous spaces beneath the surface, sheltered from the harsh conditions above.
Could these hidden structures change the way humanity explores the Moon? And what might scientists discover when they finally investigate one directly?
The mysterious opening scientists want to investigate
The target of the new investigation is the Marius Hills Pit, located in a region shaped by ancient lunar volcanism. Unlike an ordinary impact crater, this feature has steep walls and characteristics that make scientists suspect it could be an opening into a subsurface structure.
The project is called the Geophysical Instruments for Marius Lunar pit Investigation, or GIMLI. Led by the Planetary Science Institute, the selected investigation is intended to use geophysical instruments and imaging to probe what lies beneath the pit. The proposed approach includes radar, seismic measurements, gravity observations and cameras to help characterize any underground void.
The crucial question is whether the opening leads into a substantial cave or lava tube—or whether the underground structure is smaller or more complicated than scientists expect.
The cave has not yet been confirmed in its entirety. The mission is designed to investigate that uncertainty, rather than explore a fully mapped underground network.
That distinction makes the project scientifically valuable. From orbit, researchers can identify unusual surface features and study indirect clues, but determining the shape, continuity and stability of a hidden cave requires more evidence.
How could a cave form on the Moon?
The most likely explanation involves the Moon’s volcanic past.
Billions of years ago, molten rock flowed across parts of the lunar surface. Under the right conditions, the outer layer of a lava stream could cool and harden while molten material continued moving beneath it. If the remaining lava eventually drained away, it could leave behind a hollow tunnel.
These structures are known as lava tubes. Similar formations exist on Earth, including in volcanic regions such as Hawaii.
Over time, sections of a tube’s ceiling can collapse, exposing an opening known as a skylight. From the surface, the opening may look like a dark pit leading nowhere, even though a larger cavity could extend beyond the visible walls.
Scientists have identified multiple pits on the Moon that may be associated with underground structures. However, not every pit necessarily leads to an extensive cave, and the dimensions and condition of any hidden tunnel must be established individually.
If the Marius Hills Pit opens into a large lava tube, it could provide an opportunity to study a part of lunar geology that has remained inaccessible to direct observation.
Scientists have already found evidence of a lunar cave
The Marius Hills investigation is not the first indication that the Moon may contain underground spaces.
In July 2024, researchers published a study in Nature Astronomy examining radar observations of the Mare Tranquillitatis Pit. The data, originally collected by NASA’s Lunar Reconnaissance Orbiter in 2010, provided evidence consistent with a cave conduit extending at least tens of metres beyond the pit.
The finding strengthened the case that some lunar pits could provide access to underground environments.
NASA has also investigated the temperatures inside lunar pits. Research published in 2022 found that shaded areas within certain pits could maintain temperatures around 17 degrees Celsius, or 63 degrees Fahrenheit, considerably more stable than the exposed lunar surface. The Moon’s surface can experience extreme temperature swings, from roughly 127 degrees Celsius in daylight to minus 173 degrees Celsius at night.
These findings do not mean every lunar pit contains a large cave. They do show why researchers consider underground lunar environments worthy of further investigation.
What might be hiding beneath the lunar surface?
The word hiding can suggest something mysterious or even artificial, but there is currently no evidence that these pits conceal alien structures or extraterrestrial activity.
The genuinely fascinating possibility is geological.
A substantial lava tube could preserve clues about the Moon’s volcanic history, including how molten rock moved beneath ancient landscapes. Its walls and floor might contain material that has experienced different environmental conditions from rocks exposed on the surface.
Underground spaces could also help scientists understand how the Moon’s crust formed and changed over billions of years.
There is another important consideration: preservation. The lunar surface is exposed to radiation, micrometeorite impacts and dramatic temperature changes. A sufficiently deep cave could offer greater protection from some of these hazards, potentially preserving geological material that is more exposed elsewhere.
Researchers would need to explore the actual structure before determining what it contains and how well its interior has been preserved.
Could astronauts one day live inside a lunar cave?
The potential implications extend beyond scientific discovery.
Future lunar missions will need to address radiation exposure, temperature extremes, abrasive dust and the challenges of transporting construction materials from Earth. A naturally occurring underground cavity could potentially reduce some of these difficulties.
Instead of constructing every protective structure from scratch, astronauts might eventually investigate whether a suitable lava tube could accommodate equipment, shelters or scientific laboratories.
NASA’s lunar-pit research has identified underground environments as potentially useful locations for future exploration, but turning that possibility into a practical habitat would require extensive engineering.
A cave would have to be surveyed for its dimensions, structural stability, accessible entrances and internal hazards. Engineers would also need to determine how astronauts and robotic equipment could safely enter and leave it.
Radiation shielding would not eliminate every risk. Lunar dust, communication limitations, power supply, emergency access and the possibility of unstable rock would all need to be addressed.
For now, an underground lunar base remains a potential future application, not an established mission plan for occupying the Marius Hills Pit.
The real mystery is what we cannot see
The Moon has been observed from Earth for thousands of years, and spacecraft have mapped much of its surface. Yet a photograph of a pit cannot reveal everything that exists beneath it.
That gap between what scientists can observe and what remains inaccessible is what makes the Marius Hills investigation so interesting.
If the proposed instruments detect a substantial underground cavity, researchers could gain a better understanding of its size and structure. If they find a smaller void—or no extensive cave at all—the result would still help refine scientific models of lunar geology.
Either outcome would improve our understanding of the Moon.
The investigation also highlights a broader principle in planetary science: familiar landscapes can conceal structures that are difficult to identify from the surface alone.
There is no evidence that the Moon’s underground pits contain alien bases or unknown civilizations. The real discovery may be remarkable enough without such speculation. A world that appears barren from above could hold an extensive geological history beneath its surface.
As scientists prepare to investigate the Marius Hills Pit, one question remains particularly compelling: how much of the Moon’s hidden landscape have we yet to discover?
