The search zone is growing smaller. Astronomers have further constrained the likely whereabouts of Planet Nine: the planet that, if it exists, is more massive than the Earth and roams the outer reaches of the solar system. In January, Konstantin Batygin and Mike Brown, two planetary scientists at the California Institute of Technology, speculated on the existence of a ninth planet based on an odd alignment of six distant icy bodies. Excitement rippled through the world of astronomers and many immediately joined the hunt.

A month later, Agnès Fienga at the Côte d’Azur Observatory in France and her colleagues found evidence that slight perturbations in Saturn’s orbit as observed by the Cassini spacecraft could be better explained by the missing planet. They were even able to suggest where Planet Nine might be along the most likely orbit proposed by Batygin and Brown. READ MORE