Researchers have found evidence for a substantial underground cave on the moon that is accessible from the surface, making the location an excellent place to build a future lunar base.
The cave is apparently accessible from an open pit in the Mare Tranquillitatis (Sea of Tranquility), the ancient lava plain where Apollo 11 astronauts Neil Armstrong and Buzz Aldrin first sat on the moon more than half a century ago.
Analysis of radar data collected by Nasa’s Lunar Reconnaissance Orbiter (LRO) has revealed that the Mare Tranquillitatis Well, the deepest known well on the Moon, leads to a cavern 45 meters wide and up to 80 meters long,’ an area equivalent to 14 tennis courts. The cave lies about 150 meters below the surface.
Lorenzo Bruzzone, of the University of Trento in Italy, said the cave was “probably an empty lava tube”, adding that such features could serve as human habitats for future explorers, as they provided a “natural shelter from the harsh lunar environment ” is.
Lunar orbiters first noticed pits on the moon more than a decade ago. Many are considered “skylights” that connect to underground caverns such as lava tubes, giant underground tunnels formed by volcanic processes.
Such caves could form the basis for a lunar base or an emergency lunar shelter because the temperature inside is relatively stable and astronauts would naturally be protected from harmful cosmic rays, solar radiation and micrometeorites.
Previous images taken from the LRO showed that the bottom of the Mare Tranquillitatis pit was littered with rocks up to 10 meters wide. But it was unclear whether the pit was sealed or served as an entry point to an underground cavern, like a lava tube whose roof had collapsed.
Write in Nature Astronomythe scientists describe how they used LRO data and computer simulations to show that the 100-meter-wide pit, bounded by vertical or overhanging walls, leads to a sloping floor and a cavern that extends tens of meters westward.
Researchers are keen to study the rocks inside such caves, as they are likely to hold clues to the moon’s formation and volcanic history. The caves may also contain water ice, a resource that Bruzzone says is essential for long-term lunar missions and colonization.
At least 200 pits have been spotted on the moon and many found on lava fields may be entrances to cavernous underground lava tubes. “The main advantage of caves is that they make available the most important structural parts of a possible human base without requiring complex construction activities,” said Leonardo Carrer, the study’s first author.
In preparation for humans’ return to the moon, space agencies are already wondering how to assess the structural stability of caves and strengthen their walls and ceilings. Habitats may also require monitoring systems to warn of movement or seismic activity and have separate areas to which astronauts can retreat if parts of their cave collapse.
“Lunar cave systems have been proposed as great places to put future crew bases, as the thick cave ceiling of rock is ideal for protecting people and infrastructure from the very fluctuating day-night lunar surface temperature variations and for blocking high-energy radiation that strikes the lunar surface,” says Katherine Joy , professor of earth sciences at the University of Manchester.
Robert Wagner, a researcher at Arizona State University, said one of the biggest challenges will be access. “To get into that pit, you have to descend 125 meters before you reach the floor, and the edge is a steep slope of loose debris where any movement will send small avalanches to anyone below,” he said. “It’s certainly possible to get in and out, but it would require a significant amount of infrastructure.”
