A team of planetary scientists from the California Institute of Technology have published a paper documenting strong circumstantial evidence for a large planet with an orbit outside of Pluto’s. This yet-undiscovered planet is hypothesized to be smaller than Neptune, but would be 10-times more massive than Earth, and comes no closer than 30.5 billion km (19 billion miles) to the Sun.
Tentatively named "Planet Nine", researchers Konstantin Batygin and Mike Brown built their finding on an earlier study that suggested that a large planet at the far reaches of the solar system was affecting the orbits of smaller planetoids in similar, far-flung orbits. Batygin and Brown analyzed the orbits of numerous trans-Neptunian objects, and found "that the long axes of these objects’ orbits fall into the same quadrant of the sky,” according to Batygin. This meant that the objects’ highly-elliptical orbits pointed in the same direction — an indicator that they were being shepherded by a larger gravitational source.
When Batygin and Brown applied a hypothetical planet to a computer simulation, the new model showed the same orbits as what was being observed with known objects in the region. On top of that, the simulation also indicated that the planet’s gravity should cause the orbits of a collection of other trans-Neptunian objects to be sharply tilted, away from the plane of the solar system. Researching this lead, they found a half-dozen such objects that had been documented, with orbits that had previously puzzled their discoverers — a puzzle that may now be solved.
If there is indeed a large planet on the far reaches of the solar system, Brown says that it could be spotted with telescopes that are in use today, such as the Japanese Subaru Telescope in Hawaii. “Unfortunately, we don’t own the Subaru,” Brown says, “which means we’re unlikely to be the ones who find it. So we’re telling everyone else where to look.”