Full Moon…full of lava tubes?
Credit: NASA/JPL

There is “mounting evidence” from a number of lunar probes that suggest the presence of vacant lava tubes under the surface of the Moon.

“Such large sub-lunarean structures would be of great benefit to future human exploration of the Moon, providing shelter from the harsh environment at the surface,” reports a Purdue University research team.

Indeed, some of those Moon tubes may be more than a kilometer in width.

Sub-surface stability

The team, led by David Blair of the Department of Earth, Atmospheric, and Planetary Sciences at Purdue, have reported on “The structural stability of lunar lava tubes,” reporting their findings in the scientific journal, Icarus.

Blair and his colleagues also tackled whether or not empty lava tubes of this size are stable under lunar conditions? Furthermore, what is the largest size at which they could remain structurally sound?

The Purdue team addressed these questions by creating “elasto-plastic finite element models” of lava tubes using the Abaqus modeling software and examining where there is local material failure in the tube’s roof.

The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than one kilometer wide could remain structurally stable on the moon.
Credit: Purdue University/courtesy of David Blair

Roof thickness

Team results show that the stability of a lava tube depends on its width, its roof thickness, and whether the rock comprising the structure begins in a lithostatic or Poisson stress state.

Taking that into account, with a roof of some seven feet (2-meters) thick, lava tubes a kilometer or more in width can remain stable, they report.

The theoretical maximum size of a lunar lava tube depends on a variety of factors, the study group says, but given sufficient burial depth of 1,640 feet (500 meters) and an initial lithostatic stress state, their results show that lava tubes up to three miles (5 kilometers) wide may be able to remain structurally stable.

Artist concept of GRAIL mission.
The twin Gravity Recovery and Interior Laboratory (GRAIL) mission of 2012 flew spacecraft in tandem orbits around the Moon to measure its gravity field in unprecedented detail.
Credit: NASA/JPL



Multi-country probing

This research made use of Japan’s SELenological and ENgineering Explorer “KAGUYA” (SELENE), the country’s first large lunar explorer, NASA’s Lunar Reconnaissance Orbiter (LRO), and especially data gleaned by the two NASA Gravity Recovery and Interior Laboratory (GRAIL) spacecraft.



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Also, check out this Inside Outer Space story on an early statement from the science team:

Tunnel Vision: Underground Cities on the Moon


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