'Planet 9' - an unseen planet on the edge of our solar system - probably formed closer to home around the Sun than previously thought, astronomers say.
Researchers in the UK found that Planet 9 is unlikely to have been captured from another planetary system, as has previously been suggested.
The outskirts of the solar system have always been something of an enigma, with astronomers in the late 19
th and early 20
th centuries searching for a giant planet that was not there, and the subsequent discovery of Pluto in 1930.
Pluto was downgraded in status to a 'dwarf planet' because astronomers discovered many other small objects so-called Edgeworth-Kuiper Belt objects at similar distances from the Sun.
Last year, astronomers working in the US postulated the presence of 'Planet 9' to explain the strange orbital properties of some Edgeworth-Kuiper Belt objects.
However, while it is not possible to directly observe Planet 9, it has not stopped theorists from trying to work out how it got there.
Planet 9: Know More- Planet 9 is at least ten times bigger than Earth, making it unlikely that it formed at such a large distance from the Sun.
- Instead, it has been suggested it either moved there from the inner regions of the Solar System, or it could have been captured when the Sun was still in its birth star cluster.
- Researchers simulated the Sun's stellar nursery where interactions are common and found that even in conditions optimised to capture free-floating planets, only five-to-10 out of 10,000 planets are captured onto an orbit like Planet 9's.
