One day the Earth had no moon, the next it was there, according to a radical new theory on the creation of our only major satellite. 

The current theory backed by most experts is that after a collision with a Mars-sized planet called Theia, rocks blasted into space eventually coalesced into the moon over hundreds or thousands of years.

Other theories – that the Earth and moon formed at the same time, or that the Earth captured the wandering moon when it got too close – have slowly been jettisoned in favour of the ‘giant impact hypothesis’ (read more about it here). 

But there are problems with the existing theory, the astronomers behind the new hypothesis say. There’s a whole lot of complicated mathematics in the paper crunched by a supercomputer, but essentially the moon’s current orbit doesn’t fit, nor does its thin crust. 

If the moon was created not over time “inside a swirl of vaporised rock from the collision”, but instead almost instantly, the calculations are “cleaner and more elegant”, they say.

“The moon may have formed immediately, in a matter of hours, when material from the Earth and Theia was launched directly into orbit after the impact,” NASA’s Ames Research Center said in a statement this week.

“This scenario can put the moon into a wide orbit with an interior that isn’t fully molten, potentially explaining properties like the Moon’s tilted orbit and thin crust – making it one of the most enticing explanations for the moon’s origins yet.”

It’s hoped when NASA’s future Artemis missions bring back rocks from the moon, scientists will get even closer to nailing down just where the moon came from. 

“The more we learn about how the moon came to be, the more we discover about the evolution of our own Earth,” said Vincent Eke of Durham University, co-author on the paper. “Their histories are intertwined – and could be echoed in the stories of other planets changed by similar or very different collisions.”

“We went into this project not knowing exactly what the outcomes of these high-resolution simulations would be,” said Jacob Kegerreis, a postdoctoral researcher at NASA’s Ames Research Center. “So, on top of the big eye-opener that standard resolutions can give you misleading answers, it was extra exciting that the new results could include a tantalisingly moon-like satellite in orbit.”