Saturday, 23 January 2016

Planet Nine: The Hunt Begins

So it was recently announced by researchers at Caltech that they believe the solar system does  have nine planets, and that the ninth planet is not Pluto, but in fact a 10 Earth-mass world orbiting up to 1200 times further out from the Sun as the Earth.

The world has been dubbed 'planet nine' and the method used by the folk at Caltech to infer its existence is robust. They have studied the orbits of several KBO's (Kuiper Belt Objects). The Kuiper belt is like the asteroid belt between Mars and Jupiter, but far bigger in extent, and contains several dwarf planets such as Pluto and Eris. Comets originate from this outer region of the solar system. By tracking the orbits of KBO's, they have determined that there must a 10 Earth-mass planet out there, exterting a gravitational pull, in order to explain the KBO orbit shapes. The image below shows the KBO orbits and the hypothetical orbit of planet nine:


This method has been used before to infer the existence of previously unknown worlds, most famously by Adams and Le Verrier in the 1800s, when they both predicted where Neptune should be before it had been observed. The problem with planet nine, is that even though it isn't a tiny planet, it is stupendously far from the Sun. This means the amount of reflected sunlight will be minuscule and even the worlds best telescopes might struggle to find it - even if they know where to look. Regardless, the hunt is on!

The publication in the Astrophysical Journal can be found here