The Unusual Beginning of the Hollow Moon Theory
- Chethana Janith
- Mar 9
- 4 min read
Chethana Janith, Jadetimes Staff
C. Janith is a Jadetimes news reporter and sub-editor covering science and geopolitics.
We break down how misinterpreted science from the Apollo moon missions gave rise to this bizarre belief.
The hollow moon conspiracy theory came about during the Apollo missions in 1969.
Conspiracy theorists misinterpreted the results of the astronauts’ seismic experiments, leading them to believe the moon was hollow.
Scientists said the moon rings “like a bell.” That’s because the vibrations from the moon’s seismic events, known as moonquakes, last much longer than those on Earth.
Conspiracy theorists once claimed that the moon was hollow. While that notion is still more plausible than the moon being made of cheese, it seems almost laughable by today’s standards. So, how did the hollow moon theory - or more accurately, conspiracy - gain traction?
Interestingly, it doesn’t stem from ancient folklore, nor is it particularly old. The hollow moon theory emerged in 1969 during the Apollo 12 moon-landing mission, as NASA researchers sought to unravel the moon’s composition. During this mission, astronauts Pete Conrad and Alan Bean deployed a Passive Seismic Experiment (PSE) at the landing site. This was part of a broader set of experiments known as the Apollo Lunar Surface Experiment Package (ALSEP).
After the Apollo 12 astronauts returned safely to the command module, they deliberately crashed the lunar module into the moon’s surface. The impact, equivalent to detonating one ton of TNT, triggered what was referred to as a “moonquake” - the first of its kind caused by human activity. The PSE seismometers captured the ensuing vibrations, which were far stronger and lasted significantly longer than the scientists had expected. These vibrations were drastically different from the earthquake patterns we’re accustomed to on Earth.
NASA extended its moonquake studies throughout the Apollo 13, 14, 15, and 16 missions, consistently observing similar results.
At the time, these findings were surprising as they suggested that the moon was much less dense than Earth. And indeed, it is - only about 60 percent as dense. While this does not imply that the moon is hollow, the unexpected data fueled conspiracy theorists, who twisted the information into the infamous hollow moon theory - just another example of how misinformation can take on a life of its own.
What Are Moonquakes?
The Passive Seismic Experiment (PSE) seismometers, deployed during the Apollo 12 mission, remained operational until 1977. They recorded both natural and human-made moonquakes, providing invaluable insights into lunar activity. Interestingly, moonquakes occur quite regularly. Unlike Earth, the moon’s sparse atmosphere allows space debris, such as asteroids, to strike its surface far more frequently.
Scientists have identified four distinct types of moonquakes: deep quakes occurring over 700 kilometers below the surface, meteorite-induced quakes, thermal quakes caused by temperature fluctuations, and shallow quakes that happen just 20 to 30 kilometers deep. Among these, shallow moonquakes - like those triggered by NASA’s experiments - are the most intense and long-lasting. Some even registered as high as 5.5 on the Richter scale. Naturally occurring shallow moonquakes also happen, but their exact causes remain a mystery.
Why Does the Moon “Ring” Like a Bell?
Here’s where scientific observation met misinterpretation. “The moon was ringing like a bell,” noted Clive R. Neal, professor of civil engineering and geological sciences at the University of Notre Dame, in a NASA write-up. From a scientific perspective, this description is apt. The vibrations recorded during moonquakes were likened to those of a tuning fork - a type of acoustic resonator - because they persisted much longer than expected. “It just keeps going and going,” Neal elaborates.
However, the moon does not literally emit bell-like sounds, nor is it hollow like one. Conspiracy theorists, however, interpreted this poetic analogy as literal fact.
On Earth, vibrations from earthquakes typically fade within 30 seconds to two minutes. This is due to the presence of water, which weakens stone and alters the structural composition of minerals. As Neal explains, “Water weakens stone, expanding the structure of different minerals. When energy propagates across such a compressible structure, it acts like a foam sponge - it deadens the vibrations.”
Conversely, the NASA-induced moonquakes lasted over ten minutes. For instance, the Apollo 12 experiment recorded shockwaves that peaked nearly eight minutes after impact and took about an hour to fully subside. This phenomenon has a straightforward explanation: the moon is significantly drier than Earth. With water largely absent, except in the form of ice, and a much more rigid structure, the moon allows seismic vibrations to resonate and persist for longer periods.
While these results were groundbreaking at the time, they’ve been crucial in advancing our understanding of the moon’s composition. Although the hollow moon theory has been thoroughly debunked, the quest for lunar knowledge continues.
Terry Hurford, a NASA geophysicist, is currently working on the Subsurface Lunar Investigation and Monitoring Experiment (SUBLIME). This project aims to map the moon’s core and further study moonquakes for the Artemis program. As Hurford states, “Our understanding of the moon’s interior remains rudimentary and is limited.”
Comments