There may be a ninth planet and again, but hold your breath kiddies, it’s not Pluto. This hypothesis has gone back as far as the following of the discovery of Neptune, most notably with Percival Lowell’s hypothesis for Planet X. His hypothesis on his mystery planet’s orbits disrupting the orbits of its neighbors, Uranus and Neptune, actually served to validate the work of Clyde Tombaugh’s discovery of Pluto, which is how we originally got our official ninth planet… for a while, anyway. The more we learned about the objects orbiting the area beyond Neptune, the more we came to understand that Pluto wasn’t categorically a planet. Before it could even complete one full revolution around the Sun, it became known as a “dwarf planet”, leaving us with eight official planets in our solar system once more. Yet evidence for a ninth planet’s growing now that the scientific community’s gleaning more information about heavenly bodies that exist in and around the region of space known as the Kuiper Belt, their orbits, and how those orbits effect other celestial bodies within the area.
The Planet Nine making headlines in 2016’s hypothesized to be an ice giant, composed of ice and rock with a pocket of gas. Its size is estimated to be two-to-four times the diameter of Earth and ten times its mass. Those measurements land Planet Nine well within the “planet” category. In 2009 a Wide Field Infrared Survey Explorer didn’t exclude such an object, and a 2014 study corroborated the possibility of higher-mass bodies in the outer solar system. Planet Nine’s orbit is hypothesized to be a length of twenty times the distance from Neptune to the Sun, its elliptical orbit having a semi-major axis of 700 AU taking around roughly 10,000-20,000 years.
These calculations and computer simulations regarding Planet Nine’s current fame are thanks to the work of California Institute of Technology’s researchers Michael Brown and Konstantin Batygin. The pair originally designed their work to refute a very strong argument for Planet Nine’s existence in a paper published by astronomers Chad Trujillo of the Hawaii’s Gemini Observatory and Scott Shepphard of The Carnegie Institute of Science in 2014. Shepphard and Trujillo’s work theorized that the orbits of sednoids – objects in the area of the Kuiper Belt – might be influenced by the orbit of a massive unknown planet at the very edge of our solar system. Not only did Brown and Batygin’s research support the 2014 findings, they were able to solidify them into a more unifying picture. Brown was even able to hypothesize what Planet Nine would have been if not flung so far from the sun during its development: It had all of the makings of a gas giant.
While it would be exciting to have a ninth planet in our solar system once again, and an ice giant at that, we’ll probably need more proof than just gravity’s shadow. Goodness knows we jumped the gun last time the scientific community decided to call a planetoid a planet, so we’d better be doubly sure this time before schoolkids start learning a new mnemonic device.