The hole is the Mare Tranquillitatis pit, a steep-sided opening in the Moon’s Sea of Tranquility. Radar data suggest it may lead into an underground passage tens of metres long, but scientists have not directly explored the passage or established the cave’s full size.
Where is the hole on the Moon?
The Mare Tranquillitatis pit lies in the Sea of Tranquility, about 230 miles northeast of the site where humans first landed on the Moon, according to NASA Science. The visible pit is a surface opening; the possible cave is a separate feature inferred below it.
How do scientists know it may open into a cave?
A 2024 peer-reviewed study reanalyzed radar images collected in 2010 by the Mini-RF instrument aboard NASA’s Lunar Reconnaissance Orbiter. The researchers found reflections consistent with a subsurface conduit tens of metres long. NASA’s summary describes the inferred passage as extending more than 200 feet from the pit base. Those figures describe the portion supported by the radar analysis, not a measured total cave length.
Radar can reveal clues about structures below the surface, but this result is not a photograph, a direct survey, or evidence that a spacecraft has entered the passage. The researchers interpreted the radar reflections as evidence for a cave-like conduit; its full dimensions and accessibility remain unknown. The primary study appeared in Nature Astronomy on July 15, 2024.
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What is known about the pit’s depth and temperature?
NASA’s 2022 analysis, based on data from the Diviner instrument, modeled the pit as approximately 100 metres deep. It found that permanently shadowed reaches of the pit remain near 17°C. This is a modeled temperature for the shadowed pit, not a direct measurement of the inferred cave interior. A passage extending from the pit could have a similarly stable environment, but that possibility has not been confirmed.
How might a lunar cave form?
One possible explanation is a collapsed section of an ancient lava tube. Lava tubes can form when flowing lava develops a cooled crust over a still-moving interior; after the lava drains away, a hollow passage remains. If part of its roof collapses, the opening can appear as a pit.
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This is a plausible mechanism for lunar pits, not a confirmed account of how the Mare Tranquillitatis pit formed. NASA’s 2014 overview of lunar pits notes that images alone offer little basis for determining the cause of an individual pit. It cataloged more than 200 lunar pits at the time; that historical figure is not a current census.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why does the possible cave matter?
A subsurface passage could help scientists investigate lunar geology and how volcanic features formed. The pit’s shadowed areas also have a relatively stable modeled temperature. Cavities might offer shelter from some conditions at the exposed surface, making them interesting to consider for future exploration.
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Those possibilities are not proof that this site is suitable for astronauts or a base. The available evidence does not establish the passage’s structural condition, its radiation environment, whether a rover or crew could enter safely, or whether a mission plan exists to explore it. As LRO project scientist and NASA Goddard Space Flight Center scientist Noah Petro put it, “Now the analysis of the Mini-RF radar data tells us how far these caves might extend.”
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