The moon may have formed from a group of smaller moonlets

A new theory claims Earth debris was blasted into space during a series of impacts.


A study published in the journal Nature Geoscience this week suggests an alternate history for Earth's celestial companion. According to the researchers behind the study, the moon isn't just one large space rock, but 20 or so smaller "moonlets" made of matter that was blasted away from Earth in a series of impacts and merged together over time into the moon we have now.

As the Washington Post reports, the new study by planetary scientists from the Weizmann Institute of Science in Israel is a big departure from the previously accepted "giant impact model." That model claims a hypothetical protoplanet called Theia smashed into the earth some 4.4 billion years ago, sending dust and debris into space that eventually formed the moon. That theory has fallen out of favor with scientists in recent years as researchers studying lunar samples from the Apollo missions have noticed they are remarkably similar to Earth's chemical makeup. If a giant object did smash into the Earth, there should be some trace of it left in the moon, and as scientists try to account for the similarities, the model starts to become less plausible. Those same Apollo samples also put the moon's age slightly older at 4.51 billion years old.

"Our model suggests that the ancient Earth once hosted a series of moons, each one formed from a different collision with the proto-Earth," study co-author Hagai Perets told Smithsonian Magazine. "It's likely that such moonlets were later ejected, or collided with Earth or with each other to form bigger moons."

The moonlets theory has actually been around since the 1980s, but Perets and his colleagues are the first to create a working model and perform the 1,000 simulations necessary to demonstrate its possibility. As co-author Raluca Rufu told the Guardian, "with 20 impactors, it would take about 100 million years to build the moon."

On the other hand, the study doesn't explain how the moonlets came together to form one supermoon. The giant impact model also helps explain how the Earth got its tilted axis, which the new theory doesn't account for. That said, the study's authors believe more lunar samples could help clear up some of the mystery and expect to have more information once China starts exploring the dark side next year.