When we talk about two moons or two suns rising simultaneously from the horizon, we most often immediately start thinking about science fiction movies based on planets that existed a “long time ago, in a galaxy far far away.”

It seems, however, that our planet also had two moons during its early years. According to the theory published by Dr. Martin Julzi and Dr. Erik Asphaug on the Nature on Aug. 8, extensive simulations support the idea of two-mooned young Earth.

This theory suggests that Earth might have been circled by two moons in the same orbit until a slow-motion collision merged the larger moon with a smaller moon about one-thirtieth of the larger body.

Such a “slow” collision at 5,000 miles per hour would have caused the smaller moon to “spread over and around the bigger moon” without creating a crater.

This theory is extremely helpful in trying to understand the “lunar dichotomy” where one side of the moon flat and is comprised of low-lying plains while the other side is heavily cratered and has mountain ranges higher than 3,000 meters. Duality is also geologically evident as the crust on the mountainous side is nearly 50 kilometers thicker than that of the flat side.

Former NASA associate Alan Stern told the CBS that this idea was a ‘very clever new idea” that would be very hard to prove with tests.