Did scientists just confirm the hollow moon conspiracy theory?

In 1969, the first humans set foot on the moon. They stepped out onto the lunar surface in an area called the Sea of Tranquility – a vast basin formed by collisions with cosmic debris and filled in with ancient lava flows. Now, more than half a century later, scientists have reported a new discovery in the famed landing zone: a mysterious opening that leads to a massive underground cave.

With NASA’s Artemis programme intending to return humanity to the moon in the 2020s, there’s already been some speculation about how the discovery could alter plans for future explorers. It could even be a prime spot for a future moon base, if we realise plans to colonise our only natural satellite.

On social media, meanwhile, there have been some even more outlandish claims, with whispers among conspiracy theorists – the ones that believe the moon actually exists and isn’t just projected on a glass dome – that it confirms a long-running hypothesis: the moon is actually hollow, and someone, or something, could already be living inside it.

Before going any further, we should note that this theory goes against any real scientific evidence. Is that going to stop us from wild speculation about a hidden society inside the moon? Of course not!

FIRST, WHAT DOES THE NEW STUDY SAY?

Published in the scientific journal Nature Astronomy on July 15, the research paper notes that hundreds of openings on the surface of the moon (or “lunar pits”) have been discovered in the past. Until now, though, we haven’t really figured out what lies beyond them: are they just deep holes, or could they provide access to a hidden network of caves that spreads much further than we can see with our telescopes?

To find out, the scientists used radar data collected by NASA’s Lunar Reconnaissance Orbiter (LRO) to explore the Mare Tranquillitatis Pit (MTP) in more detail. What they found was pretty solid evidence of a cave that begins around 150 metres beneath the surface, measuring an estimated 80 metres long and 45 metres wide (that’s about three times the area of an Olympic swimming pool). The cause, they suggest, is likely the collapse of a long-defunct lava tube, suggesting there might be more all across the moon’s crust.

AND WHAT’S THE HOLLOW MOON THEORY AGAIN?

On the most basic level, the hollow moon theory is exactly what it sounds like: the moon is hollow, and its inner vault is accessible via hidden entrances on the outside. Like most conspiracy theories, though, the idea has evolved over the years. Sci-fi writers such as HG Wells imagined that the hollow moon was inhabited by a race of sophisticated aliens as early as 1901.

Another theory, dating back to an article in the Soviet Sputnik magazine in the late 60s and endorsed by the likes of David Icke, says that an alien civilisation actually invented the moon. According to this theory, the moon is a “very ancient spaceship” that, for some unknown reason, decided to park up in Earth’s orbit.

Then, there are the theories prompted by Nazi science experiments during World War II. These blend hollow Earth conspiracies (a bunch of baddies secretly survived and now reside deep inside our home planet) with Nazi UFO theories, to suggest that Hitler and friends are alive and thriving inside an artificial or hollowed-out moon, waiting for the right time to stage their return.

WHERE’S THE EVIDENCE?

This is an important question. During the Apollo 12 mission in 1969, which was the second to land on the moon, humanity caused its very first ‘moonquake’ by crashing an unmanned module into the lunar surface. These experiments continued across future moon missions, and the results were quite unexpected.

During moonquakes, the moon itself vibrated much longer and more heavily than expected. Even relatively small vibrations “caused the Moon to ring like a bell for several hours,” said NASA. That’s all the ‘evidence’ that hollow moon truthers needed to back up their arguments... and basically the only evidence they’ve received ever since.

Even then, the “ring like a bell” statement has been discredited as a poetic exaggeration of the actual effects. Yes, moonquakes vibrated much longer than your regular earthquake, but modern science suggests that this is just because the moon is so dry, whereas Earth’s high water content deadens the vibrations caused by seismic activity. And no, the moon didn’t literally ring out like a bell. At least, that’s what Big Space wants you to think.

SO IT’S NOT ACTUALLY HOLLOW, THEN?

Using today’s technology and methods, we’ve learned a lot more about the moon, like the fact that it’s shrinking and that it has a solid metal ball at its core, covered with a layer of molten metal. There are still some unexplained anomalies in the moon’s composition, but these are thought to be the remnants of collisions in the history of the rocky body’s formation, not a race of underground aliens or futuristic fascists.

As NASA geophysicist Terry Hurford says: “Our understanding of the moon’s interior remains rudimentary and is limited.” However, we understand at least enough to know that it isn’t totally hollow.

IN THAT CASE, WHY IS THE MOON CAVE SUCH A BIG DEAL?

We’ll be the first to say it: it’s slightly disappointing to learn that the moon isn’t a giant spaceship, or the subterranean lair of some sneaky extraterrestrials. There’s still plenty to be excited about though, according to the authors of the new study. “This discovery suggests that the MTP is a promising site for a lunar base,” the authors write, “as it offers shelter from the harsh surface environment and could support long-term human exploration of the Moon.”

That might sound like we’re regressing back to the Stone Age, but the point is that an existing underground structure could save a lot of time and resources. It could replace artificial habitats needed to shield lunar explorers from cosmic radiation, solar activity, and stray space debris, for example. Its hidden structures could also teach us a lot about how the moon was formed in the first place.

With a massive drop from the rim to the floor of the pit, it would of course require some significant building work. We’d also want to make sure the cave was stable, to avoid any sci-fi horror scenarios unfolding for potential inhabitants. That’s assuming human astronauts are the only inhabitants when we finally get there, and we don’t inadvertently stumble into a sprawling interior ruled by little green men.