Humanity may once again find itself living in caves after a new study out of Japan found evidence that the moon is home to caves and possibly tubes cut out from lava, which could protect future astronauts from harmful space radiation. 

Human bodies weren't made for space. We have evolved under the protection of our magnetic field, which keeps dangerous cosmic radiation from reaching us. 

However, we are entering a space-faring age, with missions to Mars and the moon announced by both NASA and SpaceX. Aside from the technological challenges faced with such goals is the challenge of protecting our fragile bodies from radiation.

One way we could do that is by using a planet — or the moon — as a shield against that radiation.

The new study, published in journal Geophysical Research Letters, suggests that a 50-kilometre long lava tube lies below a hole at Marius Hills on the moon. This would make an ideal place not only for further studying the history of the moon, but it could also provide the site for a home with ample protection for future astronauts. And there are many more possible sites.

Lava tubes

Images of a possible lunar lava tube with a diameter of 65 metres in the Marius Hills taken by the SELENE Terrain Camera and Multi-band Imager. (JAXA/SELENE)

"More than 23 locations, candidate sites of possible subsurface caves, were detected in this area," Tetsuya Kaku, lead author of the study, told CBC News.

The Japanese researchers used radar echo data from the Lunar Radar Sounder on board the SELENE spacecraft (also known by the Japanese name Kaguya) as well as the U.S. Lunar Reconnaissance Orbiter (LRO) and the Gravity Recovery and Interior Laboratory (GRAIL) in order to determine whether ancient lava flows left behind tubes deep below the surface of the moon. And they found one.

Lava flowed freely on the moon in a period of lunar volcanism more than two billion years ago. It cut channels through the rock, then eventually bubbled up and sealed them off, creating tubes — in some places, like the one discussed in the paper, 75 metres deep. Eventually, something, such as a nearby impact by a meteorite, caused part of the roof to collapse, revealing the tube.

Robert Wagner, of Arizona State University, who worked on the LRO, said the finding of the Marius Hills hole was an exciting discovery.

"Just knowing that these tubes actually exist is confirming theories that have been built up since the Apollo days," he told CBC News. "We can see surface features that hint at these lava tubes, but this is the first direct observations that there's probably a hole down there somewhere."

Future moonbase?

Wagner said he has hopes that one day humans can use these caves — even if they're not all lava tubes — to settle on the moon. In his research, he's found that they would provide adequate protection.

"In theory, there should be some path that you can either walk down or wriggle down," he said. "Spelunking on Earth involves a lot of contortionism, and it may be the same on the moon except you'll have to do it with a spacesuit."



Once humans have "spelunked" on the moon, they wouldn't necessarily have to dig through the metres of rock to build a home. 

"We know these pits exist, we know their dimensions. Even if they don't connect to a cave, they're still somewhat protective against cosmic waves, because you're down in a hole," Wagner said.

"There are a handful of the 200-odd [pits] we know about that are deep enough and narrow enough that you could actually stick a small habitation module in them and be almost as safe from cosmic rays as we are here on Earth."