For decades, evidence has accumulated to suggest a planet, or perhaps a failed star, lurks in the outer regions of our solar system. The study is the result of the work carried out by scientists at University of Arizona who in their paper have presented compelling evidence of a yet-to-be-discovered planetary body that has mass somewhere between that of Mars and Earth.
The Kuiper Belt lies beyond the orbit of Neptune and hosts a vast number of minor planets, mostly small, icy bodies and a few dwarf planets.
The Caltech team first hypothesized the existence of Planet Nine based on the odd orbital plane of six Kuiper Belt Objects (KBOs). Most sky surveys avoid the crowded orbital plane to gain unfettered views of the universe beyond our solar system. This leaves a big mystery about what could be causing this unusual tilt, and so far all signs point toward something massive...something that could have the mass of Mars.
Researchers Kat Volk and Renu Malhotra studied the orbits of objects in the Kuiper Belt, the asteroid field where Pluto is located. Each had to contend with reduced visibility due to bad weather in some seasons, and the fact that it's easier to see Kuiper belt objects away from the plane of the Milky Way. Most of the objects were angled away from their "orbital plane", meaning that something close by was messing with their orbits. The tilted orbital planes of most KBOs average out to something called the invariable plane of the solar system. "There is a range of uncertainties for the measured warp, but there is not more than 1 or 2 percent chance that this warp is merely a statistical fluke of the limited observational sample of KBOs".
Scientists at the University of Arizona believe an "unseen planetary-mass object" might be orbiting the sun in our solar system beyond Pluto. The official definition of a planet, as voted by the International Astronomical Union in 2006, is "a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit". If Planet 10 does exist it'll only be a matter of time until we find it. Both Malhotra and Volk state that finding more planetary objects within the solar system give more credence to their data. That something might be something large and something heavy, Volk said.
"A passing star would draw all the "spinning tops" in one direction", Malhotra said. There are several sky surveys like Pan-STARRS and NEOWISE that should have picked it up. Their Large Synoptic Telescope (LSST) which is now being under construction in Chile, will be the one to find them, researchers seem certain.