We’re closing in on Planet Nine. (Or X. Whatever.)

Wired (with a little help from Cassini) narrows our search for the hidden, big planet orbiting the fringes of the solar system:

Matthew J. Holman and Matthew J. Payne of the Harvard-Smithsonian Center for Astrophysics analysed data recorded by Cassini about its relative position to ground stations on the Earth during its investigation of Saturn. These figures were then used to model the likelihood of a potential ninth planet existing in a wide range of different positions.

Speaking to New Scientist, Payne said that “we put Planet Nine at a whole different slew of locations – all different possibilities on the sky, different distances, different masses – and tried to find out whether that constrains things even more.”

The research indicates that the most probable location for Planet Nine is towards the constellation of Cetus, in a patch sky with a 20-degree radius near Aires and Pisces, centred at the celestial coordinates right ascension 40?, declination -15?.

The existence of a hypothetical Planet X in the outer solar system has been posited by scientists since the 18th century, leading to the discovery of Uranus, Neptune and Pluto. But it’s only since 2014, when astronomers Chad Trujillo and Scott Sheppard observed unusual orbital behaviours in Kuiper Belt objects, that there’s been serious evidence for a full-sized planet beyond Pluto.