Scientists Discover Lava Tubes That Could Shelter Future Colonists

There is no forgiveness on the moon. Surface temperatures fluctuated by hundreds of degrees, micrometeoroids and cosmic radiation were constantly falling, and two weeks of uninterrupted sunshine were followed by two weeks of complete darkness. Engineers are anxious in this type of setting, and accountants are even more anxious. It has always seemed idealistic on paper to build a base out there on the open regolith, but it would be disastrous in reality. For this reason, the conversation has quietly begun to shift due to the gradual accumulation of evidence surrounding lunar lava tubes.

The cavern found close to the Marius Hills skylight is the headline discovery that frequently comes up in briefings and conference discussions. There, years ago, JAXA’s Kaguya orbiter detected a strange echo pattern—the kind of signal that results from radio waves reflecting off a hollow space instead of solid rock. The numbers held up when Purdue researchers used gravity data from NASA’s GRAIL mission to cross-check the location. Where you would anticipate a long, deserted tunnel to be, there is a dip in gravity. They estimated it to be large enough to completely engulf Philadelphia.

People are often interrupted in mid-sentence by that detail. Since the lunar mantle was still young, there was a void on the moon that was about the size of a large American city, waiting. When a flow of molten rock cools on top while the river below continues to flow, lava tubes are created. When the flow finally stops, you are left with a stone tunnel that can be ridiculously large or modest. They are hiking destinations on Earth. They can reach difficult-to-imagine scales on the Moon, where there is only a sixth of the gravity.

This appeal might be oversold. Although the radar and gravity work is convincing and we have identified pits and skylights, no one has actually descended into one. Mapping a likely cavern from orbit is not the same as verifying that it is dry, navigable, structurally sound, and not, say, partially collapsed. Jim Green, the chief scientist at NASA, has essentially stated that we must confirm and enter the area. The rest is just educated guesswork until a rover or a tethered probe descends through one of those skylights.

However, the reasoning is difficult to refute. Radiation shielding is necessary for surface habitats, which can be achieved by pouring lunar concrete, hauling up mass, or scraping together regolith. The shielding is provided for free by a lava tube. Cosmic rays and impacts are handled in a single stroke by tens of meters of basalt above. Instead of the harsh extremes you experience at the surface, the temperature inside remains remarkably constant, somewhere in the comfortable middle. A near-shirtsleeve climate is maintained year-round in some of these holes, according to researchers studying lunar pits at Arizona State. This is the kind of free lunch you hardly ever get in space architecture.

Determining the playbook includes the work at Idaho’s Craters of the Moon National Monument. In order to determine the true three-dimensional appearance of these features, NASA scientists have been LIDAR mapping Indian Tunnel, a lava tube that the Shoshone and Bannock peoples used for shelter and cool storage. The fact that the same type of cave is being scanned for the same fundamental purpose that it served a millennium ago seems appropriate. Shelter is shelter. Eventually, the team intends to equip rovers with scaled-down versions of that scanning apparatus and send them somewhere completely devoid of atmosphere.

In the long run, Mars is the greater prize. There have also been reports of suspected tube networks, and the radiation and dust storms on the red planet make the case for going underground even more compelling. It’s another matter entirely whether any of them are sufficiently usable by humans. The interiors must not be choked with debris or flooded with frozen volatiles, the floors must be stable, and the skylights must be accessible. Until something climbs in and surveys the area, we won’t know. Observing this gradual accumulation of data gives the impression that the next ten years of lunar exploration will be more determined by what we discover beneath the surface than by what we plant on it.