Planet Nine… is it really there? Ever since the discovery of Pluto and then its subsequent demotion to dwarf planet status, astronomers have been on the hunt for yet more denizens of the outer solar system. The Edgeworth-Kuiper Belt, initially theory and then proven to exist, stretching out from beyond the orbit of Neptune, appears to be a happy hunting ground not only for comets and other interlopers, but an increasing number of these smaller “worlds”.
Worlds like Eris, Sedna (we use ‘worlds’ here in the loosest possible way as they are as small as, or in the same region of size as Pluto) are fascinating, but what is interesting astronomers more and more over the past few years is a real “Planet 9”, something large enough to warrant being called a planet, and to take over Pluto’s lost mantle.
Studies by people of the calibre of Mike Brown, the discoverer of some of the earlier “Pluto killers”, using computer simulations have indicated that a planet up to 10 times the size of Earth, may exist out as far as 600 AU (600 times the distance from the Earth to the Sun) away. The problem is finding it. When you’re looking at what is most likely a rocky body, emitting no light of its own, probably consisting of very dark rock on the surface, at those kind of distances, you need vast telescopes, or vast amounts of telescope time on the like of the Hubble.
Objects are already being found out at tremendous distances, some only a few hundred miles wide, in “highly unusual” orbits, ones which are increasingly pointing to the existence of a ninth planet. Mathematics, much as with the discovery of Neptune, will play a key role here. As fitting these orbits to match where the ninth planet may be is key. A blind random search could take hundreds of years, but a targeted search, if more of these smaller objects, which seem to have focus points which are pointing towards the ninth planet, then that search area narrows significantly.
Many cried when Pluto was demoted, and despite the incredible work of Alan Stern and his team on New Horizons, and the truly stunning images they sent back, Pluto remains a “dwarf” in the solar system. Whilst some still fight to have Pluto reinstated, the excitement now grows almost daily that a genuine “ninth” planet may be written back in to the school textbooks, and children all over the world will have to learn a new mnemonic.