For a bizarre coincidence, I’ve written about the fabled (and infamous) Planet X just this time last year, mentioning that, from the analysis of some ETNOs (Extreme Trans-Neptunian Objects), there was some evidence of unknown gravitational pull affecting their orbit.
More specifically, of the fact that “some invisible forces are altering the distribution of the orbital elements of the ETNO and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto.The exact number is uncertain, given that the data that we have is limited, but our calculations suggest that there are at least two planets, and probably more, within the confines of our solar system.” (Carlos de la Fuente Marcos, University Complutense of Madrid).
Well, it seems they got it right, even though it is the case to stress that we’re still talking theories -as of today, they have done it through mathematical modelling and computer simulations, and not a direct observation. But at Caltech, people look moderately optimistic. “This would be a real ninth planet. There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.” (Mike Brown) The planet is supposed to have a mass about 10 times that of Earth (5,000 times the one of Pluto’s, just to be clear. So no discussions here about getting the status of a planet or not) and to orbit about 20 times farther from the sun than Neptune (whose orbit is at an average distance of 2.8 billion miles). If you do the maths, it would take Planet 9 about 10,000 -20,000 years to complete one orbit: nothing strange it has not detected before.
Brown’s article about the newfound(?) planet is an interesting reading. Reference: Konstantin Batygin and Michael E. Brown (2016) EVIDENCE FOR A DISTANT GIANT PLANET IN THE SOLAR SYSTEM, The Astronomical Journal, Volume 151, Number 2, The American Astronomical Society, available here.
And while we wait for a confirmation and some imagery, you can watch the interview with Jim Green (NASA) about the story.