Scientists Explain Key Wrinkle in Moon's Formation

How did our moon come to be? The dominant theory holds that it broke off of the Earth when another planet collided with ours, about 4.5 billion years ago. But if that's the case, it seems suspicious to scientists that the moon is made of material very like Earth's; that fact would seem to have required the planet that smacked into Earth, referred to as Theia, the Smithsonian reports, to also have been made of such material. And there's only about a 1% chance of that—or so experts thought, Nature reports. But new findings say the collision theory doesn't necessarily depend on a one-in-a-100 chance.

Researchers simulated solar systems' development and found that bodies that crashed into each other had often developed comparably close to the sun, the Smithsonian reports. The odds of such a collision, between similarly constructed bodies, may actually be more like 20% to 40%, researchers find, per Nature. "If they are living in the same neighborhood, they will be made of roughly the same material," says a researcher; "they grew up in the same environment." But the physics of the apparent collision remain a mystery, another expert tells the Washington Post: "The origin of the moon is still hotly debated." (In other moon mysteries explained, a video shows the body's "dark" side.)