Our Moon May Have Formed After a Gigantic Crash of Planets
published during a waning gibbous moon.

New evidence points to the moon emerging from a massive head-on collision.

moon formation

The final stages of planet formation were a violent and chaotic time, leaving scars that are seen throughout the solar system. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

When the moon hits another planet, it’s not exactly Dean Martin’s amore: It’s a magnificent, universe-altering smash. A collision is believed to form the moon as we know it, but a paper published online in Science this week reports the crash was head-on instead of an aggressive shoulder-check as previously reported.

A brief timeline of our chaotic beginnings: Earth is thought to have formed roughly 4.6 billion years ago. Now, its collision with an impactor called Theia, which was roughly the size of Mars, happened about 100 million years later. If you have trouble picturing what that might look like, here’s quick video of what the collision at a 45-degree angle:

After analyzing rocks collected from the moon and volcanic rocks from Earth, a team led by University of California, Los Angeles researchers suggest their chemical make-up is stronger evidence for a more direct impact. The key to the discovery? Oxygen.

Earth’s oxygen is referred to as O-16 because each atom has eight protons and eight neutrons. This is where not snoozing open-eyed in your high school chemistry class comes in handy: Though our oxygen is mostly O-16, there are tiny quantities of heavier isotopes, like O-17 (one extra neutron) and O-18 (you guessed it: two extra neutrons).

Our home planet, Mars, and other planets in our solar system each have a unique ratio of these isotopes. But the researchers found no difference between Earth’s and the moons isotopes, according to a release. If Theia had bumped into Earth, the moon would have been composed of mostly Theia. But because the chemical composition is mixed pretty evenly into both Earth and our lunar pal, it’s more likely Earth and Theia engulfed one another with some heavy amore.