Large caves on the Moon have recently been found, which emphasizes the significance of caves for astrobiology as well as for upcoming space exploration.
In 2010, after analyzing radar images captured by the Lunar Reconnaissance Orbiter, Leonardo Carrer and his team discovered that a deep pit identified 15 years earlier in the Sea of Tranquility—the area where Apollo 11 astronauts made their historic landing—seems to connect to an underground cave system extending tens of meters. The researchers suggest that this site could be a promising candidate for a future lunar base. “”
While we usually picture lunar bases on the Moon’s surface, the intense radiation and extreme temperature fluctuations might require astronauts to reside several meters below ground. A natural cave with a wide entrance could eliminate the need for extensive digging. Indeed, many space agencies around the world have long-term goals to establish bases on the Moon. Although the Sea of Tranquility lacks some of the benefits found in other locations, such as the Aitken Basin, it holds historical importance as the landing site of the first manned mission to the Moon.
From a scientific perspective, the basalt layers in this region may hold clues from a time when volcanic activity on the Moon was at its peak around three and a half billion years ago. The outgassing during this period might have been so intense that it briefly created an atmosphere about one percent the thickness of Earth’s, potentially allowing a short-lived window of habitability where microbial life could have existed for a brief time. While uncovering evidence in the basalt to support this hypothesis would be challenging, exploring a lunar cave could still offer invaluable insights into the Moon’s geological, meteorological, and environmental history.
Exploring caves on Mars is even more thrilling, as they could still serve as habitats for life today. Thousands of potential cave entrances have been detected on the planet, including “skylights,” deep fractures, pit craters, and other voids. Although it’s challenging to determine the depth of these caves from orbital images, many are likely to extend deep into the subsurface. A significant number of these caves are lava tubes, a type that is also commonly found on Earth.
An example is the Lava River Cave in Coconino National Forest, northern Arizona, a mile-long cave that formed 700,000 years ago when molten rock erupted from a volcanic vent. The outer layers of the lava flow cooled and hardened first, creating a tube through which the lava continued to flow. Similar processes have almost certainly taken place on Mars, where the caves are likely to be larger than those on Earth due to the planet’s lower gravity.
Similar to the Moon, caves on Mars would offer protection from radiation and extreme temperature variations, though these issues are less severe on Mars than on the Moon. The atmospheric pressure inside these caves would be higher than on the Martian surface, and if liquid water exists within, it could serve as a potential refuge for microbial life. This water would also be a crucial resource for human explorers.
In 2015, during the First Landing Site/Exploration Zone Workshop for Human Missions to the Surface of Mars, organized by the Lunar and Planetary Institute in Houston, I was part of a team proposing that the caves in Hebrus Valles would make an ideal site for the first human outpost on Mars. We suggested that the subsurface caverns and steep valley walls could be adapted for construction, and the potential presence of remnant water ice would be valuable for its astrobiological potential and as a resource for astronauts.
Speculation about caves beyond Earth extends further. A research team led by Michael Malaska from the Jet Propulsion Lab suggested that recurring hydrocarbon rains on Saturn’s moon Titan could form subsurface channels. By analyzing data from the Cassini orbiter, they cataloged various terrains on Titan that might contain entry points to underground spaces and identified over 21,000 potential cave locations. Other promising places to search for extraterrestrial caves include Pluto, Enceladus, and Triton.
Resources
- Apollo 11, July 1969: First men on the Moon
Air Power History, Vol. 36, No. 2 (Summer 1989), pp. 31–33
Air Force Historical Foundation - Late-stage magmatic outgassing from a volatile-depleted Moon
By: James M. D. Day, Frédéric Moynier, and Charles K. Shearer
Proceedings of the National Academy of Sciences of the United States of America, Vol. 114, No. 36 (September 5, 2017), pp. 9547–9551
National Academy of Sciences - Prospective Lava Tubes at Hellas Planitia
By: Antonio J. Paris, Evan T. Davies, Laurence Tognetti, and Carly Zahniser
Journal of the Washington Academy of Sciences, Vol. 105, No. 3 (Fall 2019), pp. 13–36
Washington Academy of Sciences - Apollo 11 Cave in Southwest Namibia: Some Observations on the Site and Its Rock Art
By: John Masson
The South African Archaeological Bulletin, Vol. 61, No. 183 (June 2006), pp. 76–89
South African Archaeological Society
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