The man in the moon is legendary, but lesser known is how he came to exist. Aside from the spacecraft and humanoids that have reached our lonely satellite, the moon has gone untouched for eons. Like footprints, the types of craters can tell us a lot about the moon’s visitors, and the man in the moon’s dark circles are the signature of a very inhospitable guest: lava.
When we see human faces in toast or clouds, it’s totally normal. Our brain is bombarded with hundreds of stimuli every day, and it’s wired to sift through and detect patterns — a phenomenon called pareidolia.
Face perception is a fast, automatic process, and it’s subconscious, too. That’s why when you stare at the moon, you can find a man’s face (or other familiar shapes, like a woman’s silhouette, or even a sleepy bunny):
Credit: D.Helber / Creative Commons
But to understand the moon man, we have to know how his body formed. A prominent theory suggests that a Mars-sized body hit Earth billions of years ago, and the remaining chunks coalesced to create the moon. The moon was molten, meaning it was home to hot, bubbling magma.
After some time, the volcanism died down, and the moon slowly crusted over and became battered into a dusty rubble by asteroids, meteors, and other space bullies.
The moon’s spots are more than just haphazard holes, though. Take a simple crater, for instance. It looks exactly as it sounds: a smooth, bowl-shaped indentation with no peak in its middle. Craters are on the smaller side, like the Martian crater below, and aren’t always visible to the naked eye. A complex crater, though, has a bit more personality—maybe a lump in the middle, or multiple rings— according to the Lunar and Planetary Institute.
This crater on northern Elysium Planitia is a little more than twice the diameter of the famous Meteor Crater in Arizona, U.S.A. It formed by the impact and subsequent explosion of a meteorite. Picture from MOC in July 1998. Credit: NASA/JPL/MSSS
There are also impact basins, which are enormous cavities that have been found on planets and moons across the galaxy. Just how big? The moon’s biggest impact basin stretches over 1,550 miles (2,500 km).
In those basins flowed lava, leaving dark basalt rocks that made them smoother and darker than the lighter highlands. Most of the basalt is in areas with the lowest elevation, especially in those massive impact basins.
And that’s the face we see looking at back at us when we look at a full moon.
Back on our planet, we have a lot of natural activity that erodes craters, like flowing water, a healthy atmosphere, and tectonic shifts — three things that the moon lacks. It’s why Earth’s face gets regular facelifts, but most of the moon’s mug is so old, it’s an ancient, preserved relic, and a glimpse into history we can’t see anywhere else.