Moon Homestay found: Nasa scientists confirm 200 caves that can shelter people, next to the Apollo 11 site where Neil Armstrong landed

Scientists have found the first solid proof of a cave hiding beneath the moon's surface, sitting just a few hundred kilometres from the spot where Neil Armstrong and Buzz Aldrin took humanity's first steps in 1969. Radar data collected by NASA's Lunar Reconnaissance Orbiter shows the cave leads off a deep pit in the Sea of Tranquility, researchers reported in the journal Nature Astronomy. The find has changed the theories about where future astronauts choose to pitch their tents.

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For at least 50 years, researchers have argued over whether the moon even has caves. Now they have an answer. And the timing works out well, because space agencies are racing to send astronauts back to the lunar surface, and those astronauts will need somewhere safe to hide from deadly radiation and brutal swings in temperature.

A Question 50 Years in the Making

Most researchers agree these hidden caves would be lava tubes, tunnels carved out by volcanic activity billions of years ago. Some pits scattered across the moon's surface might work like skylights, offering a peek into the tunnels below. NASA's Lunar Reconnaissance Orbiter first spotted such pits back in 2012, but nobody could say for certain whether any of them actually led anywhere. Researchers have now catalogued more than 200 of these pits. That changed when a team went digging through old radar data.

An Old Photo Reveals a New Secret

The breakthrough came from an unlikely source: radar images captured back in 2010 and left largely untouched for over a decade. Researchers zeroed in on a pit in the Sea of Tranquility, first spotted in 2009 and still the deepest known pit on the moon. The hole stretches more than 300 feet across at its widest point. Its walls slope downward before turning nearly vertical, dropping to a floor that sits between 410 and 443 feet below the surface.

Buried in that old radar data, the team found exactly what they were looking for: proof of a cave, at least 130 feet wide, stretching tens of yards or more, according to Marcia Dunn of the Associated Press.

A separate account of the find, published on the European Space Agency's blog, describes the cave conduit stretching more than 100 metres below the surface, with overhanging walls plunging 75 metres deep. "There are hundreds of caves on the Moon, but this is the most striking one we have detected to date. We instantly realised it had a remarkable depth, and it looked accessible at the same time," says Riccardo Pozzobon, co-author of the paper and an instructor in ESA's PANGAEA geology training programme for astronauts.

A Ready-Made Shelter for Astronauts

The discovery matters for one big reason: real estate. Future moon bases will need protection from a hostile environment, and nature may have already built it for them.

"Lunar cave systems have been proposed as great places to site future crewed bases, as 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 planetary scientist at the University of Manchester who was not involved in the research, tells the Guardian's Ian Sample. "However, we currently know very little about the underground structures below these pit entrances."

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The moon's weaker gravity, roughly a sixth of Earth's, means these caves can grow larger and are less prone to collapse, according to the ESA blog. That rock ceiling could also hide something more practical than shelter. Underground spaces may hold water ice and other frozen chemical deposits, useful for drinking water and even for making rocket fuel for the trip home, per the ESA blog post.

Study co-author Wes Patterson, a planetary geologist at Johns Hopkins University, says the discovery proves old data can still deliver new answers.

"This research demonstrates both how radar data of the moon can be used in novel ways to address fundamental questions for science and exploration and how crucial it is to continue collecting remotely sensed data of the moon," he tells the Independent's Andrew Griffin. "This includes the current LRO mission and, hopefully, future orbiter missions."

Getting In Won't Be Easy

Not everyone is ready to book a room just yet. Other scientists point out that reaching this particular cave will be no small feat.

"Getting into that pit requires descending 125 meters before you reach the floor, and the rim is a steep slope of loose debris where any movement will send little avalanches down on to anyone below," Robert Wagner, a research specialist at Arizona State University who did not contribute to the findings, told the Guardian. "It's certainly possible to get in and out, but it will take a significant amount of infrastructure."

Helen Sharman, the first British astronaut to travel to space, offers a more colourful fix. Astronauts might need to use "jet packs or a lift" to get out of the cave, she told BBC News.

Why It's Worth the Trouble

Beyond shelter, the caves could hold scientific gold. Studying them could help researchers piece together how volcanic activity shaped the moon in its early days, and every new pit found adds another candidate site for a future base, tucked safely away from cosmic radiation and the moon's punishing temperature swings.

Back on Earth, the European Space Agency is already training astronauts for the job through its CAVES course, which sends crews underground to practice working as teams before they ever leave the planet.

"Space exploration will require future crews to become surface explorers again. CAVES is evolving to give them just the right skills," says Loredana Bessone, the course's director, on the ESA blog.

For now, humanity has a new hole to obsess over, one that sits practically next door to the most famous footprints in the solar system.