After Decades of Theories, We Finally Know What’s Inside the Moon

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