Lunar lava tubes as the first Moon homes

Lunar Lava Tubes and Why the First Moon Homes May Be Underground

Most pictures of a future Moon base show shiny domes or stacked modules sitting on gray soil. This page argues for a different first step: the earliest long-term homes on the Moon may be natural caves left behind by ancient lava flows, because those caves already provide much of the shelter that a surface base would have to build and ship at great expense. The page serves the futurism and abundance goals of this wiki. It asks how people could move from a world where every kilogram sent to space is scarce and costly toward a settlement that uses what the Moon already offers, and it treats that idea as an open research question rather than a promise.

What a lunar lava tube is

On Earth, a lava tube forms when the outer skin of a lava flow cools and hardens while hot lava keeps moving underneath. When the flow drains away, a long hollow tunnel is left behind. NASA explains that scientists suspect the Moon formed caves the same way, and that when part of a tube ceiling collapses, it opens a pit that works like a skylight into the tunnel below.

The first lunar pit was confirmed in 2009 from images taken by the Japanese Kaguya orbiter, and many more have been found since by NASA's Lunar Reconnaissance Orbiter. News coverage of the 2024 findings reported that more than 200 pits are now known.

The 2024 evidence that a real cave exists

For years, a pit was only a hole, and nobody could say whether it led anywhere. In July 2024, a team led by the University of Trento published radar evidence in Nature Astronomy. They reanalyzed radar images of the Mare Tranquillitatis pit collected in 2010 by the Mini-RF instrument on the Lunar Reconnaissance Orbiter, and found that part of the radar reflections could be explained by a cave conduit tens of meters long beneath the surface. NASA described it as a cave extending more than 200 feet from the base of the pit, located about 230 miles northeast of the Apollo 11 landing site, with a full extent that is unknown and could stretch for miles.

A researcher on the team at the University of Padua said the width is at least 55 to 60 meters and could be several hundred meters or more. That is a space wide enough to hold several large buildings side by side.

Why a cave changes the cost of living on the Moon

The Moon surface is hostile in three ways that are expensive to fix with engineering alone.

Temperature swings. NASA reports that the surface heats to about 127 degrees Celsius during the day and falls to about minus 173 degrees Celsius at night. Shaded parts of the Mare Tranquillitatis pit stay near 17 degrees Celsius, about 63 degrees Fahrenheit. The study behind that finding estimated that a cave extending from such a pit would vary by less than 1 degree Celsius over an entire lunar day. A habitat that does not need to survive a 300 degree swing every month needs less heating, less cooling, and less power.

Radiation. The Chinese Chang'e 4 lander carried a German-built instrument that made the first direct radiation measurements on the lunar surface. During its first two lunar days in 2019 it measured an average dose equivalent of 1,369 microsieverts per day, and the galactic cosmic ray dose on the surface was about 2.6 times higher than inside the International Space Station. A later analysis of five years of data found that solar particle events can raise the surface dose rate by 10 to 100 times for a period. Researchers on the cave study note that caves could protect against cosmic rays, solar radiation, and micrometeorites.

Shielding mass. On the surface, protection against radiation and impacts means piling up material or launching heavy walls. In a cave, the rock ceiling is already in place. That is the core of the abundance argument. Space settlement has been limited by the scarcity and cost of lifting mass out of Earth's gravity, and a natural shelter turns part of that scarce, purchased resource into one that is simply found.

A shift from building to scouting

If caves work as hoped, the hard early problem is not construction but exploration: finding which pits connect to stable tunnels, how strong the ceilings are, and how people and machines get down safely. The European Space Agency has studied a mission concept in which a rover first scouts the rim of a pit for a safe access point, and then a probe is lowered into the pit to measure its walls and look inside.

People are already practicing on Earth. The ESA PANGAEA course trains astronauts as field geologists, including traverses in the volcanic terrain of Lanzarote, Spain. A report on the program describes training in the La Corona lava tube in 2016, 2017, and 2018 with five ESA astronauts and one cosmonaut, plus a 2017 test campaign that tried lidar mapping, ground electrical surveys for hidden cavities, and other cave exploration tools. This work also benefits people on Earth, because cave mapping and remote sensing tools improve geology, hazard study, and the search for groundwater.

Honest limits

• Only a small part of one cave has been detected. Its length, ceiling strength, and floor condition are unknown.
• Radar evidence from orbit is indirect. No rover or person has entered a lunar cave.
• The most studied pit sits near the equator, while many current mission plans focus on the south polar region for its ice. A good cave and a good water supply may not be in the same place.
• Getting down a pit with vertical or overhanging walls is a serious engineering problem, and moonquakes or ceiling collapse are risks that need study.
• A cave reduces some costs but does not remove the need for air, water, power, food, and transport from Earth or from local resources.
• Lunar caves may hold scientific value as untouched records of volcanic history, which raises questions about how much they should be altered by settlement.

Research questions worth pursuing

• Which other lunar pits show radar or thermal signs of a connected cave, and how could existing orbital data be reanalyzed to find them?
• How thick does a rock ceiling need to be to bring radiation exposure close to levels considered acceptable for long stays?
• What is the least costly way to lower people, equipment, and power lines into a pit and bring them back out?
• How could a cave habitat be sealed and pressurized, and would inflatable structures inside a tunnel be simpler than sealing the rock?
• Which lessons from Earth lava tube exploration transfer directly, and which fail in low gravity and vacuum?

Discussion questions, essay ideas, and learning related AI prompt ideas

• Explain why a natural cave might lower the cost of a Moon settlement more than a better rocket would, and where that argument could be wrong.
• Compare living underground on the Moon with living in underground spaces on Earth, such as cave dwellings and mines, and describe what each teaches about health and daily life.
• Describe how the scarcity of launch mass has shaped every space settlement plan so far, and how using local shelter could change that pattern.
• Explain how old satellite data that sat unused for more than a decade led to a new discovery, and what that suggests about open scientific data.
• Debate whether lunar caves should be protected as scientific sites before anyone is allowed to build in them.
• Design a step by step robotic exploration plan for a single lunar pit, and identify the riskiest step.
• Ask an AI system to quiz me on the difference between absorbed dose and dose equivalent using the lunar radiation measurements on this page.

See also

• Asteroid mining and water
• Self-replicating machines
• Backing up civilization
• 3D-printed houses
• Lunar BoomTown
• Outer space
• Post-scarcity economy