Lava tubes are formed by lava flowing through a volcanic vent beneath a hardened surface. If the lava empties, it leaves behind a cave, typically in a long worm-like shape. These tubes have been spotted on Earth, on Mars and on the Moon. On Earth these structures range in diameter between 10 to 100 meters in diameter. Because there appears to be a strong correlation between gravity and tube-depth, Martian tubes are estimated to be 100 times wider, and lunar tubes 1,000 times wider.
In a new study, “Lava tubes on Earth, Moon and Mars: A review of their size and morphology revealed by comparative planetology,” a team of researchers from Italian universities has assembled a database of tubes and potential tubes. Typically, they leave long, sinuous channels that can be spotted on the surface. Sometimes, they leave cave openings.
“We measured the size and gathered the morphology of lunar and Martian collapse chains (collapsed lava tubes), using digital terrain models, which we obtained through satellite stereoscopic images and laser altimetry taken by interplanetary probes,” said Riccardo Pozzobon, as reported by Universe Today. “We then compared these data to topographic studies about similar collapse chains on the Earth’s surface and to laser scans of the inside of lava tubes in Lanzarote and the Galapagos. These data allowed us to establish a … relationship between collapse chains and subsurface cavities that are still intact.”
Many scientists have suggested that lava tubes on the Moon may make favorable spots for human habitation because they would be protected from cosmic and solar radiation and they would experience less temperature variability between long lunar days and nights. A major concern, however, is how stable the structures are. Many orbital photographs show collapsed tubes. The Italians believe they are most likely stable, thanks to low gravity on the Moon. Collapses are likely due to meteor impacts.
NASA is working on plans for robotic exploration of the tubes. The proposed “Moon Diver” mission would use a rover tethered to a lander to explore the tubes. Thelander would land near a skylight, then a tethered rover would climb its way down to the tube floor.