Will some kind of life hide in these underground habitats? Will they be the first cities of the human settlers built below the surface?
Lava tubes form when the surface of flowing lava cools and hardens, but the lava in the lower layer continues to flow and can remain hot and drain, leaving a cave many kilometers long. Here on Earth, the longest and deepest lava tube that we know of is the Kazamura Cave in Hawaii (USA), 40 miles long.
Since the 1960s it has been speculated that these formations could also exist on Mars and the Moon, something that in recent years has been confirmed by the orbiters sent on different missions.
Now in a new study, the researchers argue that it is time to explore them in detail and consider them as a very likely habitat for future settlers.
“The largest lava tubes on Earth are a maximum of 40 meters wide and high,” says one of the authors, Riccardo Pozzobon, a geoscientist at the University of Padua (Italy). “And they can stretch for tens of meters like a highway below the surface.”
Rover prototype wheel in a lava tube on the island of Lanzarote in the Canary Islands, Spain. Part of a training campaign to explore formations on our planet that may be similar to those on the Moon and Mars. Credit: ESA / Robbie Shone
That is certainly large enough for multiple people to enter. But In mars, collapsed lava tubes are approximately 80 times larger than on our planet, with diameters between 40 and 400 meters. In the moon, on the other hand, they are even more colossal, with diameters between 300 and 700 times greater than those of the Earth and with a distance of up to 900 meters.
“A lava tube on the Moon could easily contain a small city within its walls,” Pozzobon explains.
Image taken by the Mars Reconnaissance Orbiter showing lava tubes on the southern flank of the Arsia Mons volcano on Mars
The enormous scale of these extraterrestrial formations is probably the result of the low Martian and lunar gravity, as well as how volcanoes functioned on these bodies compared to Earth.
To assess the size of the lunar and Martian lava tubes, the researchers collected 3D laser scans of the terrestrial tubes, both collapsed and intact. They then collected all the available satellite images of collapsed lava tubes on Mars and the Moon and modeled the size of the intact tubes based on the relationships between the destroyed and intact tunnels on Earth.
Habitats for settlers
These formations are ideal as human habitats for a number of reasons. First, they offer protection against meteors, which don’t burn as easily in the thin atmospheres of Mars and the Moon. They also contain useful chemicals such as water ice and volatiles that can be used as fuel. A thick layer of rock as a roof can also safeguard against solar radiation. And lastly, the skylights on these tubes mean a quick exit to the surface.
Occasionally science fiction authors like Kim Stanley Robinson have envisioned pressurizing craters or lava tubes, filling them with breathable air. But Pozzobon thinks that scenario is unlikely, especially in lunar lava tubes, whose entrances can be as wide as a football field.
One of the books where it is proposed to pressurize lava tubes
“Due to its enormous size and the possibility of having leaks caused by fractures in the rocks, I see this of pressurization as unlikely,” says the scientist. “It would be more likely to establish settlements within these caverns, either to house humans or to store equipment.”
However, even putting a base inside a lava tube presents a challenge.
Lava tube on the Moon
“Although a lava tube could provide a shelter from thermal oscillation, radiation and micro-impacts, it is not easily accessible and the basalt rocks inside can be razor sharp and the terrain is very uneven,” Pozzobon said. . “The engineering challenge of locating inflatable habitats there is not trivial and requires very detailed preliminary studies.”
Further exploration of the tubes
The immediate challenge is to gather more information about the lava tubes that are intact on both the Moon and Mars. For now, these structures can only be identified thanks to satellite images, locating skylights or collapses. But differentiating a skylight from a simple hole in the ground is difficult.
Models suggest that Martian lava tubes have grown to the point of collapse when the planet was geologically active, so it might be harder to find them intact. Instead, a large proportion of the lunar counterparts would be structurally safe, making them better candidates to be explored.
At the moment, there is no rover autonomous enough to practice extraterrestrial caving. And before designing and launching one to carry out such a task, satellites equipped with ground-penetrating radars or other remote technology should construct accurate maps over these underground formations.
“The process of discovering ideal sites for sublunar or submarine habitability will take a long time and many intermediate steps,” the researchers conclude.
Source: Live Science
