By 1972, twelve American astronauts had walked on the moon, and they brought home bags of its rocks. Those rocks were supposed to settle where the moon came from. Instead they made the question harder, and they left room for a much stranger answer: the moon is hollow, and somebody parks spaceships inside it.
Brothers, brides and mud
People have always told their own versions. The Luhya people of Kenya say the sun and moon were brothers, and the moon was the older and far brighter one. The jealous younger sun taunted him into a fight. The two wrestled into the mud, which dimmed the moon's glow, until God got fed up and split them. The sun got the day, and the mud-spattered moon got the night. In a Native American tale, the sun is a powerful chieftain and the moon is his beloved bride, and together they're the parents of the stars. The trouble is that the sun wants to eat his children. So the stars flee at every dawn, and each month Mother Moon turns her face away to grieve the ones he gobbled up. That's the waning moon.
Then there's the modern legend, spun by a random guy on social media named Kyle. In his version, the moon is an artificial body, an enormous hollow garage where aliens dock their ships, with a huge door hidden on the side we never see. Kyle has more company than anyone might expect, and the idea isn't new. H.G. Wells put an advanced race of insect-like creatures called Selenites inside the moon in his 1901 novel The First Men in the Moon. At the end, a scientist who has been sending telegraph messages home from inside the moon goes silent for good.
Four theories, one survivor
Science has some odd facts to explain. The moon is much less dense than Earth, so it probably has no heavy iron core. Its rocks hold very little water, maybe because the sun baked the surface. The moon has even less atmosphere than Applebee's. And oxygen isotopes, the slightly different atomic versions of oxygen, are just as common on the moon as on Earth, which suggests both formed at the same distance from the sun.
The fission theory says the young Earth was spinning so wildly that a chunk tore off and flew into orbit. It's tidy, but molten debris would have fallen back to Earth or ended up circling the sun. It wouldn't casually settle around Earth. Condensation, or co-formation, says the two took shape side by side inside a nebula, a vast cloud of dust and gas. NASA once turned Hubble images of the Helix Nebula into sound, and it sounds like monsters screaming. But twins made from the same ingredients shouldn't be so different. Capture theory says the moon formed somewhere else, drifted too close and got snagged by Earth's gravity. Capture is real, but it can't work with something as big as the moon.
That leaves the great impact theory. An object about the size of Mars slammed into the young Earth, and some of the debris stayed in orbit and clumped together into the moon. Scientists have been chewing on this one since at least the 1980s, and better computer modeling has pushed it to the top of the pile.
Rocks that match too well
Then came the samples. Moon rocks and Earth rocks are basically indistinguishable, and under the impact theory they shouldn't be. They'd only match if whatever hit Earth was nearly identical in makeup, formed at about the same time and the same distance from the sun, and carried exactly the right isotope of tungsten. That isotope comes only from the radioactive decay of hafnium, an element that was common only in the solar system's first 60 million years. The coincidence is so big that even astronomers think it's improbable.
We went to the moon and brought back rocks to solve where it came from, and they made the mystery deeper. Moon rocks are basically identical to Earth rocks, a coincidence so unlikely under the leading theory that even astronomers doubt it.
Ringing like a bell
The modern hollow-moon idea started with Apollo 12. Astronauts Pete Conrad and Alan Bean set up a seismic experiment on the surface, went back to the command module and deliberately crashed the lunar module into the moon with the force of a ton of dynamite. The moonquake that followed was bigger and longer than anything recorded on Earth. A quake here fades in 30 seconds to two minutes. NASA's moonquakes lasted anywhere from ten minutes to an hour. Clive R. Neal, a civil engineering and geological science professor at Notre Dame, said the moon was ringing like a bell and compared it to a tuning fork: "They just kept going, going, going." He blamed the difference on water, which deadens vibrations. Earth has plenty of water, and the moon has far less, though it does have some. Trillions of gallons may be trapped in tiny glass beads scattered across its surface, probably delivered by asteroids, according to research published in Nature Geoscience in March 2023. But once a scientist had said the moon rang like a bell, the hollow-moon theory took off.
Fifty years of lunar detention
After six successful landings, the Apollo missions stopped in 1972. MIT says the original moonshot was a Cold War race against the Soviet Union, built on shortcuts and costly one-time technology. That corner-cutting nearly killed the Apollo 13 crew when an oxygen tank exploded. Others call the program a hugely expensive PR stunt for a Kennedy administration still stinging from the Bay of Pigs. Presidents serve eight years at most, while a moon mission can take ten or more, so no politician wants to fight for a project that won't finish on their watch. Then the space shuttle program lost Challenger in 1986, along with a New Hampshire schoolteacher who was on board, and lost Columbia in 2003.
That's the official story. The other story says that from the very first landing, NASA found the moon already taken: an alien fleet running an artificial docking and surveillance station on the dark side, the side forever hidden from Earth. Presumably unimpressed by foil-wrapped spacecraft and Neil Armstrong bopping around singing "Yippity hoppity," the aliens decided to put the goofy earth monkeys in their place and banned humanity for 50 years, starting in 1972.
That makes the recent timing interesting. India's Chandrayaan mission launched on July 14, 2023, headed for the moon's south pole. Russia's Luna 25 followed. In 2019, China landed on the dark side, a first for any human or human-made machine. NASA and the Canadian Space Agency planned their Artemis program to send four astronauts around the moon in 2024 and to put humans back on the surface in 2025. Maybe it's one more coincidence stacked on all the others. Whatever the moon turns out to be, Earth needs it.
