Each of the solar system’s 178 moons tells a story. Whether they started as planetary twins or as wayward rocks captured by a planet’s gravity, these natural satellites can be as geologically active, weather-beaten or just plain weird as any planet. Here are a few.
Earth
Scientists only recently learned that our moon is mostly made of the same basic material as Earth, likely a result of its troubled birth. As our planet was forming, astronomers think it collided with a Mars-sized body they’ve named Theia. The two crashed so spectacularly that the resulting debris had significant chunks of both bodies. This, plus the fact that Earth and Theia were close enough in composition to begin with, meant that when the debris coalesced and formed the moon, it had a lot in common with Earth’s surface.
