Mystery orbits in solar system not caused by Planet Nine, say scientists

Highlights: Planet Nine is a proposed planet in the outer reaches of our solar system It was known to have gravitational effects on a group of trans-Neptunian Objects (TNOs) that lie beyond Neptune A new study says that a disc ten times heavier than Earth is the real cause, not Planet Nine   Planet Nine, as you may have read before, is a proposed planet in the outer rim of the solar system. Until now it was believed that its gravitational effects caused an unusual clustering of orbits for a group of trans-Neptunian Objects (TNOs), which lie beyond Neptune. According to a new study, that is not the case. The real cause of the forming of these 'mystery orbits' is a disc of small, icy bodies that weigh ten times more than Earth. The study, published in the Astronomical Journal, was put forward by scientists at the University of Cambridge and the American University of Beirut. "The Planet Nine hypothesis is a fascinating one, but if the hypothesised ninth planet exists, it has so far avoided detection," said Antranik Sefilian, a co-author of the study and a PhD student in Cambridge's Department of Applied Mathematics and Theoretical Physics. "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," added Sefilian. While exploring the possibility of a disc, Sefilian, under the guidance of Professor Jihad Touma, was able to identify ranges in the disc's mass, its 'roundness' (or eccentricity), and forced gradual shifts in its orientations. "While we don't have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we're investigating other possibilities," commented Sefilian. "It's also possible that both things could be true -- there could be a massive disc and a ninth planet. With the discovery of each new TNO, we gather more evidence that might help explain their behaviour." The mystery of Planet Nine then, is a hard one to crack.   Related Read: NASA's spacecraft's New Year plans are literally out of this world

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