The Big Splash

Night after night, the moon glows in the sky. It might be a full moon, a crescent, or entirely dark. We know it’s always there, even on cloudy nights when we can’t see it. But did you know that scientists aren’t sure how the moon came to be? They do have some ideas, though. One of the most popular theories is nicknamed The Big Splash.

If you could go back in time billions of years, our solar system would look very different. The sun was new. The planets had not yet formed. Instead, they were whirling clouds of gas, dust and rocks. As they circled the sun, gravity pulled the rocky bits together. They slowly became protoplanets, which is a sort of baby planet. This is when the Big Splash might have happened.

This is what scientists think: Earth was one of the protoplanets forming in the solar system about 4.5 billion years ago. Nearby was Theia (THEE-ah), another protoplanet. It was nearly the size Mars is now. Earth and Theia were in each other’s paths. One day, as the two were circling the sun, they smashed into each other. The energy created by the crash was incredibly powerful. It had 100 million times more energy than the asteroid impact that caused the dinosaurs’ extinction (which happened much, much later).

Earth was really, really hot at the time. Scientists think its temperature could have reached more than 3,600° Fahrenheit. It was so hot that most of Earth’s surface was liquid rock, called magma. The crash between Theia and Earth tossed magma from Earth’s surface into space. Theia was smashed to bits. Over time, all the chunks and pieces floating in space cooled and clumped up together in Earth’s orbit. They became the moon.

The theory is called The Big Splash because Theia splashed into Earth’s liquid rock surface. Scientists believe it might have happened that way because of tests done on rocks collected from the moon. The tests show moon rocks are made up of a lot of the same stuff as Earth rocks. Scientists think that’s because the moon formed from pieces of Earth that were tossed out at the time of the crash.

It makes sense, but there’s no way to know for sure.  Other scientists think the moon might have formed on its own, like Earth did. Some say both Earth and the moon were made when some other, larger protoplanets smashed together. It’s even possible the moon formed somewhere else and then was sucked into Earth’s orbit as Earth went by.

What scientists think changes as they learn more. One day we may have the technology to say exactly how the moon formed. For now, we must make our best guess.