The moon may have been created by many small moonlets that came together after Mars collided with Earth millions of years ago, a recent study in the journal Nature Geoscience reports.
This new idea — known as the multiple impact theory — challenges the popular hypotheses that the moon is the result of one giant impact. The new theory suggests that during the early days of the Earth, 20 small cosmic objects struck the planet and caused debris to fly into orbit. That debris then formed a series of disks around Earth that were similar to Saturn’s rings.
From that point, tidal interactions slowly caused the disks to form into moonlets that slowly migrated away from our planet and settled at what is known as the Hill radius.
Though past theories have offered different scenarios for moon formation, none have been able to explain why the moon and the Earth have similar compositions. However, in the early solar system, planetary impacts were quite common. So, it is much more likely that a series of impacts formed the moon rather than one unique collision.
“[T]he composition similarity between the Earth and the moon in the giant impact cannot be explained without using a special Earth-like impactor,” said lead author Raluca Rufu, a researcher at the Weizmann Institute of Science in Israel, according to Space.com. “However, if multiple of bodies contribute to the final moon, their chemical signatures can even out, therefore the traces of the various impacts will be masked.”
An international team of astronomers ran a number of numerical simulations on moon-forming processes. This revealed that the multiple-impact scenario better explains the moon’s Earthly composition than any other theory and that there is no evidence to suggest the single-impact hypothesis is more credible.
“I think this made a pretty compelling case,” said Robin Canup, an astrophysicist at the Southwest Research Institute in Boulder, Colorado, according to The Christian Science Monitor. “[A]ll of the other ideas we’ve been pursuing, while they have their differences, have all focused on the idea that a single impact produced the moon. And all of those existing models have at least an element, and in some cases multiple elements, that we think are low-probability. Given that, exploring out-of-the-box ideas is very important and needed, and I see this as one.”