Astronomers propose a new hypothetical planet, Planet Y, beyond Neptune, based on observed orbital anomalies in the Kuiper ...

A study suggests an Earth-sized planet, dubbed Planet Y, may exist beyond Neptune, affecting the orbits of icy objects in the ...

A mysterious new world may be hiding in the outer reaches of our solar system. According to arecent study published on arXiv ...

It’s “the most planet-y of the planets in the whole solar system,” said Brown, who is famous for helping demote Pluto to a dwarf planet. Related: Exoplanet hunters made key finds in 2015 ...

Searching for Planet X, Y and Z Space.com: Astronomers haven't yet found the fabled Planet X, but they are increasingly confident that such a 10th planet exists — in fact, several of them.

"Planet X" might actually exist — and so might "Planet Y." At least two planets larger than Earth likely lurk in the dark depths of space far beyond Pluto, just waiting to be discovered, a new ...

A huge planet might be sitting at the edge of our solar system without ever being seen. The world — which could be about ten times as massive as Earth — would be large enough to become the ...

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the distant solar system. The object, which the researchers have nicknamed Planet Nine, has a ...

“Planet Nine” could explain the seemingly puzzling orbits traced by two of the distant worlds, known as Sedna and 2012 VP113 (which has been nicknamed “Planet Biden” in homage to a ...

With a mass likely to be 5,000 times Pluto's and a gravitational influence that dominates an enormous orbit, Brown says it's "the most planet-y of the planets in the whole Solar System." ...