The first cave has been discovered on the Moon: is it ready to be occupied?

For the first time, a tunnel has been identified beneath the surface of the Moon, on the Sea of ​​Tranquility, where humans first set foot. While this location is not conducive to building a future colony, where there is one cave, there are likely others, which strengthens the prospects for future colonization.

Despite falling launch costs, getting heavy objects to the Moon in the near future will be very expensive. A long-term base, let alone a permanent one, will depend on being able to source as much of the supplies as possible on site. In recent years, the focus has been on finding water sources, but shelter is also crucial.

To stay on the Moon for long periods of time, future astronauts will need significant protection from space radiation and significant temperature fluctuations. We would also like to have equipment that is durable enough to survive a small collision with an asteroid, as is often the case without atmospheric protection. It would be much better if natural formations provided this protection than having to build or dig our own.

“In 2010, as part of NASA’s ongoing Luna Reconnaissance Orbiter (LRO) mission, the Miniature Radio-Frequency (Mini-RF) instrument acquired data that included a pit in Mare Tranquility“Years later, we reanalyzed these data with sophisticated signal processing techniques that we recently developed and discovered radar reflections from the pit area that are best explained by an underground conduit in a cave. This discovery provides the first direct evidence of an accessible lava tube beneath the surface of the Moon.”

The pit studied by Bruzzone and his colleagues, known as the Mare Tranquillitatis pit, is one of more than 200 that have been observed. Some or all appear to be the result of the collapse of the ceiling of a lava tube. However, the fact that such a pit exists does not mean that there is an underground cave large enough to be useful.

The Mare Tranquillitatis trench is the deepest known, so it seemed like a good place to start. It is about 100 metres in diameter and its walls are so steep that they can overhang. This makes it one of the few trenches large enough for internal features to be detected with the resolution that the LRO radar could provide.

The new study reveals a bright spot on the western side of the pit in images from LRO’s Lateral Orbital Synthetic Aperture Radar. Simulations suggest it’s a conduit 30 to 80 meters (98 to 262 feet) long and about 45 meters (148 feet) wide. Not big enough to house a city perhaps, but a suitable location for a lunar village. The cave floor is supposed to be flat enough to be usable. Although it’s more than 100 meters (328 feet) from the cave entrance to the surface, in the lunar’s low gravity it wouldn’t be a major obstacle.

The authors constructed two models of the probable dimensions of the pit and the cave, differing mainly in the height of the pile of rocks produced when the ceiling of the pit collapsed and therefore in the slope of the floor.

As is often said of New York, the Sea of ​​Tranquility is a beautiful place to visit, but we wouldn’t want to live there. That’s because it lacks the other essential ingredient for lunar habitation: ice. Frozen water almost certainly exists at the lunar poles, particularly the South Pole, which inspired the race to land on that planet.

The ice near the surface of the equatorial plain of the Sea of ​​Tranquility would have long since boiled during the days of lunar heat. The nostalgia of being about 7 degrees north of where Armstrong took “one small step” will not compensate for having nothing to drink.

The work, however, increases the chances that such lava tubes could exist at the poles and, more importantly, that they could be found from space with slightly improved resolution. “These caves have been theorized for over 50 years, but this is the first time we’ve demonstrated their existence,” Bruzzone said.

The study is published in Nature Astronomy.