Lunar pits are steep-sided depressions or openings in the Moon’s surface. Some expose overhangs or voids, and radar evidence indicates that the Mare Tranquillitatis pit opens onto a conduit extending more than 200 feet from its base. That makes lunar caves a credible possibility—but it does not mean every pit leads to a cave, or that a large underground network has been mapped.
What is a lunar pit?
A lunar pit is a depression or opening in the Moon’s surface, often with steep walls. A pit that exposes an underground void is sometimes called a skylight. The terms describe what can be seen at the surface; they do not, by themselves, establish how the feature formed or how far any void continues below ground.
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NASA reported more than 200 lunar pits in a 2014 inventory, with diameters ranging from about 5 meters to more than 900 meters. Those figures describe that report’s inventory, not a current count. The pits NASA discussed occur in lunar maria, impact-melt settings and highlands. NASA’s 2014 overview of lunar pits notes that images alone may not reveal a pit’s origin.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsHow might pits connect to caves?
Lava tubes
One plausible explanation for some lunar voids is volcanic lava-tube formation. Lava can flow beneath a hardened surface crust; if the molten material drains away, a hollow passage may remain. If part of its roof later collapses, the opening can appear at the surface as a pit or skylight.
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This is a proposed mechanism for some pits, not a settled explanation for every one. NASA also discusses the possibility of voids forming in impact-melt ponds. A pit’s appearance alone is not enough to determine which process produced it.
Visible openings are not complete cave maps
NASA’s 2022 account describes overhangs at two prominent pits that clearly lead to caves or voids, and strong evidence for a possible large cave at another. These observations support the existence of underground spaces, but an overhang or visible opening does not establish the full dimensions or continuity of a cave. NASA’s account of lunar pits, overhangs and temperature modeling also quotes UCLA researcher Tyler Horvath estimating that about 16 of the more than 200 pits were probably collapsed lava tubes. That is Horvath’s estimate as reported in 2022—not evidence that all pits are lava-tube entrances.
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What does the Mare Tranquillitatis pit reveal?
The clearest named evidence for a subsurface conduit comes from the Mare Tranquillitatis pit. An international team reanalyzed Mini-RF radar data collected by NASA’s Lunar Reconnaissance Orbiter in 2010. NASA’s July 18, 2024 summary of the analysis reports evidence of a cave extending more than 200 feet from the pit’s base. The full extent is unknown, and the conduit could continue farther beneath the lunar mare.
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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →The result supports the idea that at least one lunar pit connects to a substantial underground void. It is not a complete survey of that cave, proof of an extensive mapped network, or evidence that other pits necessarily have the same structure. See the NASA summary of the 2024 radar finding and the associated Nature Astronomy paper.
Could lunar caves offer a more stable environment?
Some evidence suggests that permanently shaded reaches of certain pits may have milder temperatures than the exposed lunar surface. Using Lunar Reconnaissance Orbiter Diviner observations and computer modeling, researchers found shaded reaches around 17 °C, as summarized by NASA in 2022. This figure applies to modeled, permanently shaded locations—not every pit, every cave, or the entire underground environment.
A comparatively stable temperature is scientifically relevant, but it does not establish that a cave is habitable, safe, or ready for human use. The cited observations do not provide a complete picture of conditions throughout a cave.
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What scientists can—and cannot—conclude
- Established: The Moon has many documented surface pits, and observations show that some expose overhangs or lead to voids.
- Supported for one named site: Radar analysis indicates a conduit extending more than 200 feet from the base of the Mare Tranquillitatis pit.
- Still unknown: The full dimensions and extent of that conduit, the origin of every pit, and whether other pits connect to comparable caves.
- Not established by these findings: A complete underground cave map or confirmed habitability.
The evidence comes from spacecraft imaging, thermal measurements and radar—not direct human exploration of the caves.
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