Subsurface tunnels beneath the lunar surface might just be excellent habitats for humans.
NASA and other space agencies have long had plans to colonize the moon. The goal is to establish a permanent base where people can stay for extended periods. This endeavor allows the acquisition of essential knowledge and experience needed for future missions to Mars. However, a crucial question remains: where exactly should future lunar colonists reside? Do the much-discussed underground moon caves exist? A new study sheds light on this question.
Lava Tunnels
The idea of living beneath the surface of the moon has been considered for quite some time. Researchers are particularly interested in empty lava tunnels, which offer significant advantages over building a base on the surface. These tunnels can protect astronauts from cosmic radiation, solar radiation, and micrometeorites. Such protection is not a luxury but a necessity as cosmic and solar radiation on the lunar surface can be up to 150 times stronger than what we experience on Earth. Additionally, temperatures within these tunnels remain stable, unlike the extreme fluctuations on the surface. Sunlit areas of the moon can reach a scorching 127 degrees Celsius, while the dark side can plummet to -173 degrees Celsius. Furthermore, these caves are often closer to sources of water ice and other essential minerals needed for long-term habitation. Although promising, it was unclear until now whether such underground moon caves genuinely existed.
So far, more than 200 ‘pits’ have been discovered on the moon’s surface. These pits emerged due to collapses of underlying lava tubes, leading to openings into subterranean cavities. A pressing question remains whether these pits provide access to extensive underground spaces suitable for housing astronauts.
Mare Tranquillitatis Pit
In a recent study, researchers analyzed radar data from the Lunar Reconnaissance Orbiter specifically focused on the Mare Tranquillitatis Pit, known as the deepest pit on the moon, with a diameter of about 100 meters. “We used radar data to investigate whether this pit harbors a hidden cave,” stated researchers Lorenzo Bruzzone and Leonardo Carrer in an interview. “We discovered that the Mare Tranquillitatis Pit indeed provides access to a cave, which we then mapped. This cave is accessible from the lunar surface. The most likely explanation for our observations is an empty lava tube.”
They Exist
This means Bruzzone and Carrer have found direct evidence of an accessible lava tunnel beneath the surface for the first time—a milestone. “For more than 50 years, lunar caves have been a mystery,” says Bruzzone. “It was thrilling to finally prove the existence of an underground passage. Interestingly, the data used in our study has been available for 14 years. As in many cases, the development of new data analysis technologies led to a new discovery by re-analyzing ‘old’ data.”
The researchers noticed an increase in radar brightness on the west side of the Mare Tranquillitatis Pit. Simulations based on the radar images concluded that these observations could be explained by the presence of a hollow space extending from the west side of the pit floor. The scientists estimate this hollow space lies at a depth of between 130 and 170 meters, measuring between 30 to 80 meters in length and about 45 meters in width. The cave might also be flat or have a slope of up to 45 degrees.
Lunar Colonists
The discovery of the lunar cave offers hope for future lunar colonists. The research indicates that underground caves not only exist but may also be habitable. The Mare Tranquillitatis Pit and its underground cavity are seen as a promising location for a future moon base. “Multiple international efforts are underway by various space agencies to investigate if such caves could be suitable as shelters,” says Carrer. “If conditions turn out to be favorable, these caves might be used as shelters in the future.”
Challenges
Thorough investigation is crucial, as living underground also comes with its challenges. “When considering housing astronauts underground on the moon, safety is the top priority,” emphasizes Carrer. “Each potential solution has its pros and cons in terms of safety. The main advantage of caves is that they provide the essential structural components for a possible human base without needing complex construction. However, potential risks must be considered and analyzed thoroughly. This includes performing detailed structural analyses to assess cave stability, reinforcing the walls and ceilings of the tunnels, establishing alternative living spaces for astronauts to move to if part of the tunnel gets damaged, and setting up monitoring systems that can detect, for instance, lunar quakes.”
Future Missions
The researchers view their study as a starting point for further exploration of lunar caves. They suggest that the method used could also be useful for investigating other moon pits and discovering multiple underground passages. However, better images of the lunar surface are required. “Unfortunately, the current available data is very limited and covers only a small part of the lunar surface,” notes Bruzzone. “Moreover, they lack the detail needed to detect small caves, which are crucial for planning a moon base. Therefore, it is essential to plan new missions consisting of satellites orbiting the moon equipped with radar instruments. We need both a radar like the one used in our recent discovery to create a detailed map of all lunar caves with sufficient resolution and a low-frequency radar probe systematically penetrating the lunar surface. This probe should be specifically designed to detect cavities and tunnels, even in locations far from the known pits.”
The study marks the first step towards understanding lunar caves as potential habitats for astronauts. It is clear, however, that much work remains to confirm their suitability for long-term habitation. Nonetheless, space agencies are optimistic. Since 2012, for example, ESA has conducted two training programs for astronauts focused on the underground systems of Lanzarote in collaboration with several European universities. So far, dozens of astronauts have received ‘cave walking’ training, with some undergoing geological field training. This demonstrates that ESA considers lava tunnels on other celestial bodies to be highly suitable as habitats. Perhaps these underground systems indeed will become the first new living environments for humans on another celestial body.
