Evidence of ninth planet orbiting our sun is announced in journal jointly published with IOPP

21 January 2016

Evidence of a new planet in our solar system orbiting 20 times further from the Sun than Neptune has been announced in The Astronomical Journal, published jointly by IOP Publishing and the American Astronomical Society.

Planet 9
Credit: iStockphoto.com

The previously undiscovered planet has not yet been directly observed but is calculated to be 10 times as massive as the Earth with an orbit taking 10,000 to 20,000 years to be completed. The planet, nicknamed Planet Nine, is thought to be 5,000 times as massive as Pluto, the solar system’s originally designated ninth planet, which was reclassified as a dwarf planet.

Researchers at Caltech made the discovery through mathematical modelling and computer simulations, prompted by unexplained features of the behaviour of 13 Kuiper Belt objects. Six of them follow elliptical orbits that all point in the same direction in space and are all pointing 30 degrees downward in the same direction relative to the plane of the eight known planets. This led on to further investigations by theorist Professor Konstantin Batygin and observer Professor Mike Brown.

The simulations pointed to a planet in an anti-aligned orbit in which its closest approach to the Sun is 180 degrees across from all the other objects and known planets. Batygin said: “Your natural response is ‘this orbital geometry can’t be right – this can’t be stable over the long term because this would cause this planet and these objects to meet and eventually collide’.” However, a mechanism known as mean-motion resonance actually prevents them from ever colliding.

Planet Nine’s existence would help explain some features of the orbit of Sedna, discovered in 2003, and simulations of its orbit successfully predicted the existence of some other Kuiper Belt objects. It would also make our solar system more similar to planetary systems that have been discovered orbiting other stars.

Brown and other colleagues are now searching for Planet Nine. Brown said: “I would love to find it, but I’d also be perfectly happy if someone else found it. That is why we’re publishing this paper. We hope that other people are going to get inspired and start searching.”

Further details of the discovery are on the IOPP website.