Planet Nine may not be a planet, but mystery about hidden solar system object remains

Scientists say that the hypothetical Planet Nine may not be the cause of irregular orbits of objects in the far solar system.

The alternative explanation, put forward by researchers at the University of Cambridge and the American University of Beirut, proposes a disk made up of small icy bodies, with a combined mass as much as ten times that of Earth.

That mass is similar to the one described to theorised ninth planet lurking in the dark distant reaches beyond Neptune.

But the new study used computer modelling to suggest that there might be a huge disc of icy objects out there instead.

Study author Antranik Sefilian, a PhD student at Cambridge said, "The Planet Nine hypothesis is a fascinating one, but if the hypothesized ninth planet exists, it has so far avoided detection.

"We wanted to see whether there could be another, less dramatic and perhaps more natural, cause for the unusual orbits we see in some TNOs.

"We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disk beyond the orbit of Neptune and see what it does for us?

"If you remove planet nine from the model, and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs."