Scientists discover an underground cave on the moon where astronauts could live, and suspect hundreds more

Scientists have confirmed, for the first time, that the moon contains a vast underground cave located on the side of a deep pit in the lunar surface.

• Scientists have the most convincing evidence yet of an underground cave on the moon. 
• The large cave could be a safe, warm place for astronauts to work and live on the moon.
• The researchers want to use radar technology to identify even more caves under the lunar surface.

In the ongoing effort to establish a permanent lunar base where humans can live and work on the moon, scientists have discovered a possible game changer: a large underground cave.

For decades, scientists have suspected the moon may harbor caves below its surface. Now, a new paper from a team of Italian researchers offers the most convincing evidence yet.

"Lunar caves have remained a mystery for over 50 years. So it was exciting to be able to finally prove the existence," authors Leonardo Carrer and Lorenzo Bruzzone of the University of Trento told The Associated Press.

The team speculates that, given how they think this cave formed, there could be hundreds more hidden under the lunar surface. Instead of building homes on the moon, we could inhabit the existing caverns beneath it.

How such a large cave formed on the moon

Judging from the data, the researchers estimate the cave is approximately 150 feet wide and up to 260 feet long, which is slightly smaller than an American football field with the end zones cut off.

The cave sits deep within a pit, called the Mare Tranquillitatis pit, which likely formed when a lava tube collapsed. The moon has no active volcanoes today, but billions of years ago, its surface was covered with lava that flowed down and through valleys, carving tubes across the lunar surface.

Over millennia, some of those tubes became unstable and collapsed, creating pits, like the one the research team studied from radar images taken by NASA's Lunar Reconnaissance Orbiter. We don't have a clear picture of what the caves look like inside, but lava tubes, like those in Hawaii, can offer some idea.

NASA's LRO has identified over 200 of these pits on the moon, suggesting there could be hundreds of underground caves, too. These caves could offer future astronauts protection against the extreme conditions on the moon's surface, the researchers reported in the paper published Monday in the peer-reviewed journal Nature Astronomy.

The pros and cons of living in moon caves

"The thick cave ceiling of rock is ideal to protect people and infrastructure from the wildly varying day-night lunar surface temperature variations and to block high energy radiation which bathes the lunar surface," Katherine Joy, a professor in earth sciences at the University of Manchester who wasn't involved with the study, told The Guardian.

Because the moon has no atmosphere to help regulate climate, its surface sees drastic temperature swings. During the day, the sun's heat bakes the lunar surface to about 250 °F and at night it can dip below -200 °F.

But in underground caves, the temperature would be both consistent and, per past research, very comfortable.

In a 2022 study of the same region — Mare Tranquillitatis — a separate team of researchers used computer simulations to suggest that permanently shadowed regions within these lunar pits, and any adjacent caves, would remain at around 63 °F.

Reaching these pits and caves is another matter. The cave inside Mare Tranquillitatis is located over 400 feet from the surface near the bottom of a steep slope lined with loose debris.

Getting up and down that slope would require some technological ingenuity, whether it's jet packs that can fly us in and out, some type of lunar elevator that can shuttle people up and down, or something else.

To the moon cave and beyond

Radar technology could help scientists identify even more caves and tubes extending from open pits on the moon's surface. In the future, a spacecraft with a higher-resolution radar could even map the interior of all the pits LRO has identified, according to the Nature paper.

Such a "complete survey" would allow them to assess the best locations for further exploration and future moon bases, the researchers wrote.

There's also a chance that moon caves harbor water, which will be a crucial resource for any future moon bases.

Scientists have long known there's frozen water on the moon — just under its surface, in its permanently shadowed craters, and even in lonely H2O molecules sprinkled across the sunlit lunar dirt, less moist than the Sahara Desert.

Since underground caves are shielded from the merciless vacuum of space and the radiation of the sun, they could have water ice, Bruzzone told the Australian Broadcasting Corporation.

Access to lunar water is key to NASA's plans to establish a permanent base on the moon and, eventually, use it to hopscotch astronauts to Mars. Water wouldn't just be for drinking; it could also be broken down into its elementary components — hydrogen for rocket fuel and oxygen for breathing.

Bruzzone and his co-authors also noted that caves and lava tubes of different ages may act like fossilized records of the moon's history. Eventually, exploring them up close could help scientists better understand volcanic activity.