If you've ever wondered how the moon ended up being marked up with so many craters, then John Chambers, an astrophysicist at the Carnegie Institution in Washington D.C., can probably satisfy your curiosity. He believes that a fifth rocky planet may have been responsible for the many impact craters on the moon's surface, before falling (and summarily being destroyed) by the sun. Sounds plausible? Read on to find out more.

Okay, so John Chambers thinks that a phantom planet did it. How would one be able to mark up the moon in such a manner that the craters can actually be seen from Earth? The answer is simple: asteroids.

The fifth rocky planet, which John Chambers refers to as Planet V, could have had an orbit that regularly passes near or through the asteroid belt of our solar system, and its gravity might have pulled a few chunks of floating rock from the asteroid belt whenever it came close.

These chunks of asteroid, now disengaged from their normal route, could have made their way into the inner orbits and crashed into other celestial bodies - one of these being the moon itself.

It's a bit far-fetched, but it does tie in neatly to an event scientists call LHB, or Late Heavy Bombardment. LHB is pretty much a point in time (around 3.9 billion years ago) when the moon and other inner planets got pelted heavily by asteroids. One only needs to look at the moon's pockmarked surface to find out just how damaging the impacts were caused.

Fellow scientist David Kring thinks that the theory itself is interesting, at it gives rise to the thought that impacting debris could have been caused by an inner planet, rather than something from the outside. Of course, it's still just a theory, as he says that the reasoning itself relies on the invention of a new planet, and that it would need further investigation before anything is confirmed.