A new study suggests yet another theory for a possible extra planet in our solar system, likely of a size between Mercury and ...

Astronomers have discovered fresh evidence suggesting the possible existence of an unseen planet in the far reaches of our solar system.

Is there a massive undiscovered planet on the outer reaches of the solar system? The idea has been around since before the discovery of Pluto in the 1930s. Labeled as planet X, prominent astronomers ...

For over a century, astronomers have wondered if there’s an extra planet in our Solar System that we haven’t been able to detect yet. It seems like we get another “Planet Nine” candidate — formerly ...

A recent study introduces the idea of Planet Y, a theoretical world that could explain strange gravitational behavior beyond ...

Scientists may have discovered a dwarf planet far beyond Neptune — an unearthing that may disprove a longstanding theory about the possibility of a giant ninth planet. The dwarf planet's existence ...

It's an evocative idea that has long bedeviled scientists: a huge and mysterious planet is lurking in the darkness at the edge of our solar system, evading all our efforts to spot it. Some astronomers ...

Earth has a newly-discovered neighbor in the solar system. But the heavenly body – possibly a dwarf planet à la Pluto – isn't a frequent visitor. Located beyond Neptune, its extreme orbit ...

Astronomers have observed a massive growth rate in a free-floating rogue planet that’s gobbling up gas and dust at a record rate of 6.6 billion tons per second.