There's a new theory about our solar system - our sun may have a long-lost twin.
Astronomers have long been puzzled by how crowded the area beyond Neptune is, which doesn't match with scientific models of how the galaxy formed.
The Oort cloud is a sphere of icy debris that is located in the outer reaches of our solar system. The area contains approximately 100 billion individual items (mostly chunks of rock and ice) which is far more than science would predict likely to be there.
Research has also suggested the potential presence of an unknown planet in the Oort cloud, whose gravity is tugging the space debris into formation, Harvard astrophysicist Avi Loeb told Live Science.
"The question is: How did [the Oort cloud debris] come to exist?" he said. "The popular view is that maybe they were scattered from the disk that made the planets."
He added that you "cannot easily explain" why the cloud contains so many objects if they all came from the inner solar system, indicating that many of them may have come from the opposite direction.
Loeb and fellow Harvward collaborator Amir Siraj have suggested that our sun may have had a twin, a second star that helped it collect passing debris from interstellar space which is now present in the crowded outer reached of the solar system.
The sun's gravity alone wouldn't have been powerful enough to pull so many objects into its orbit, so maybe a second star of about the same size helped out.
The theory says that at some point in the distant past, the twin broke away from its orbit and has ended up in a completely different region of space. But its influence remains in the Oort cloud.
Loeb says the second sun theory could explain not just the huge number of items in the cloud, but also the strange spherical shape they formed inside it, rather than the disk shape other items in the solar system form.
"The beautiful thing is we can test it," he said.
If the sun really did have a twin, we'll never find it, he added, as the Milky Way has rotated and shifted far too much since the twins split.
If the theory proves correct, it means there should be a great number of dwarf planets still orbiting somewhere in the galaxy that were once caught up in the two suns' orbit.
The much-anticipated Large Synoptic Survey Telescope, due to be completed in 2021, will have the ability to scan the sky in unprecedented detail and may be able to locate such dwarf planets and prove the twin sun theory correct.