The evidence for and against Planet 9

'Planet Y' theory hints at hidden Earth-size world lurking in the solar system — and it could be much closer to us than 'Planet Nine'

An Astronomer Has Found the Hardest Evidence Yet for the Elusive Planet Nine

'Planet Nine': New study reveals high probability of ninth planet in solar system

Caltech Researchers Find Evidence of a Real Ninth Planet

How Scientists (Possibly) Found the Solar System's Ninth Planet

Planet Nine by Team Nova, Daniel Power, Ronan Richardson, Jake Stephens, Chorliehere, Marcus Ellis

Inside the Search for Planet Nine

Think You Can Find Planet 9? Check Out This Citizen-Science Project