Competing ideas abound for how Earth got its moon
Earth's satellite may have formed from one giant impact or from about 20 small ones
By
Thomas Sumner
6:00am, April 4, 2017
The moon’s origin story does not add up. Most scientists think that the moon formed in the earliest days of the solar system, around 4.5 billion years ago, when a Mars-sized protoplanet called Theia whacked into the young Earth. The collision sent debris from both worlds hurling into orbit, where the rubble eventually mingled and combined to form the moon.
If that happened, scientists expect that Theia’s contribution would give the moon a different composition from Earth’s. Yet studies of lunar rocks show that Earth and its moon are compositionally identical. That fact throws a wrench into the planet-on-planet impact narrative.
https://www.sciencenews.org/article/earth-moon-formation-impact?mode=topic&context=36
