The Moon's surface is a harsh and unforgiving environment, with extreme temperature fluctuations that can reach up to 127°C during the day and drop to -173°C at night. However, a recent study by scientists at UCLA has revealed a potential solution to this challenge: permanently shaded parts of certain lunar pits remain at a relatively constant temperature of around 17°C. This discovery has significant implications for humanity's future on the Moon, as it suggests that our first permanent lunar address may be underground.
The study, led by planetary scientist Tyler Horvath, used data from the Diviner Lunar Radiometer Experiment aboard NASA's Lunar Reconnaissance Orbiter to measure the temperature of pits in Mare Tranquillitatis and Mare Ingenii. The results showed that protected parts of these pits remain at a steady temperature of 17°C, with only small variations. This is a powerful argument for building below ground, where a natural rock roof can moderate temperature and protect against other hazards.
One of the key advantages of building underground is the natural thermal buffer provided by the pit's geometry. With almost no atmosphere to redistribute heat, the lunar ground responds directly to sunlight and darkness. The Sun remains above the horizon for about 15 Earth days at many locations, after which it disappears for another 15. Loose regolith warms rapidly in daylight and radiates energy into space after sunset. However, a pit's geometry changes which surfaces can see the Sun and cold space, creating a natural thermal buffer before engineers add any machinery.
The study also highlights the potential for these pits to lead into ancient lava tubes. Pits were first identified on the Moon in 2009, and some occur in impact melt, while others in volcanic plains probably formed when sections of lava-tube roof collapsed. The Lunar Reconnaissance Orbiter Camera gallery shows that the Tranquillitatis pit floor extends at least 25 meters beneath the visible surface, proving a recess, not a vast continuous tunnel. However, the size and stability of each void, its formation history, and whether a robot can reach it safely remain major unknowns.
While temperature is a significant advantage, it is not the only one. A sufficiently thick roof could reduce exposure to galactic cosmic rays, solar particle events, and micrometeorite impacts. It could also limit contamination by electrically charged dust lofted near the surface and protect equipment from direct ultraviolet radiation. However, every benefit introduces an engineering question, such as the potential for unstable walls or loose boulders, the need for reliable access, lighting, communications, emergency escape, and structural maps.
The cave contains no breathable atmosphere, and turning part of a lava tube into one pressurised room would require seals able to withstand outward force across cracks and porous rock. A more likely early approach would place conventional pressure vessels inside the shelter, using the cave as a protective outer building rather than attempting to fill the whole void with air. Power also becomes complicated underground, with solar arrays needing exposure above the rim, and cables or stored energy brought down to the habitat.
The next decisive measurement cannot come from a conventional overhead image. A robotic scout would need to descend by tether, rappel down a wall, or deploy small hopping and rolling machines. It would map the void with lidar and radar, measure radiation and temperature, inspect fractures, and determine whether the cave continues beyond the entrance. Later thermal modelling has expanded the question to latitude, pit shape, and the survival of volatile compounds, with a 2023 study showing that not all caves share the same conditions.
The scientific reward would extend beyond settlement. Lava-tube walls may expose stacked flows that record the Moon's volcanic history, and shielded surfaces could preserve ancient material with less disturbance from impacts and radiation. A cave mission would study both a potential home and an archive. However, the headline says humanity's first permanent lunar address 'may' be underground, rather than predicting that it will be, as there are still many unknowns and engineering challenges to overcome.
In conclusion, the discovery of permanently shaded parts of lunar pits at a constant temperature of 17°C is a significant development in our understanding of the Moon's environment. While it provides a compelling argument for building underground, there are still many unknowns and engineering challenges to overcome before we can establish a permanent lunar address. A robotic scout will be crucial in determining whether there is a stable room at the end of the shaft, and in exploring the potential for ancient lava tubes and their preservation of the Moon's history.
