Studies Illuminate the Moon's Explosive Origin

A trio of new studies has breathed life back into a dramatic theory about the birth of the moon. Scientists have long suspected that the moon was formed when a Mars-sized planet called Theia smashed into Earth, obliterating itself and creating the moon, the LA Times explains. The problem? The moon is geologically identical to Earth, making it hard to believe it's leftovers from another world. Here's how new studies are changing that belief:

• The first, published in Science posits that the Earth was spinning incredibly fast back then, with days lasting just two to three hours. At that speed, the collision might destroy both worlds, and the two bodies would mix together to form the moon.
• The second study, also published in Science, hypothesizes that two planets of about the same size might have collided and mixed together to form the Earth, throwing the moon off in the process. Such an impact would have sped up the Earth's rotation, but the first study shows how that rotation could have been slowed down since.
• Another study published in Nature analyzed rocks brought back from the Apollo missions, and concluded that lots of water boiled away during the moon's birth, Space.com reports. That implies "a big event with lots of energy," supporting the impact theory, a geochemist tells the Times.

(More moon stories.)