For decades, conspiracy theorists have claimed the Moon might be hollow. Some said it was an alien base. Others swore it “rang like a bell” when Apollo astronauts dropped debris on it, arguing that it couldn’t be solid. The truth is far less cinematic, but still fascinating. Scientists have finally confirmed what’s actually inside the Moon: a solid metal heart surrounded by molten rock.
The study, published in Nature, combined years of laser ranging, gravity mapping, and Apollo-era seismic data. Led by Arthur Briaud of France’s National Centre for Scientific Research, the team found that the Moon’s inner core is solid with a density close to iron. It measures about 258 kilometers in radius and sits within a molten outer layer roughly 360 kilometers thick—essentially a scaled-down version of Earth’s core.
That finding changes what we thought we knew about the Moon’s past. For years, scientists have debated whether its center was molten or solid. Briaud’s model ends the argument and helps explain how the Moon once generated a magnetic field strong enough to magnetize ancient rocks before fading billions of years ago.
What’s Inside the Moon?
Magnetic fields are born from movement in molten metal. Confirming the Moon’s layered core lets researchers estimate when its internal “dynamo” began and when it finally went still. Geological evidence suggests it was active more than 3.5 billion years ago, slowly weakening by around 3.2 billion years ago.
The study also supports a phenomenon called mantle overturn, where dense material sinks toward the center while lighter material rises. It’s a slow-motion mixing of the Moon’s interior that may account for the iron-rich volcanic regions scattered across its surface. In other words, the Moon was once far more active than its calm exterior suggests.
Future missions could settle the details. Better seismometers and new laser reflectors could track subtle moonquakes and map its interior in real time. For now, the mystery that launched decades of speculation has an answer. The Moon isn’t hollow, haunted, or hiding aliens. It’s solid, molten, and a lot like Earth.
The post After Decades of Theories, We Finally Know What’s Inside the Moon appeared first on VICE.
