The small world was found during a search for the hypothetical Planet Nine, and astronomers say the next time it will reach ...

It's an evocative idea that has long bedeviled scientists: a huge and mysterious planet is lurking in the darkness at the ...

For decades, our solar system was thought to have nine planets, with Pluto considered the smallest and farthest. But in 2006, ...

U.S. astronomers hunting for "Planet Nine" have instead stumbled on what appears to be a new dwarf planet in the solar system's outer reaches.

In the cold, dark outskirts of planetary systems far beyond the reach of the known planets, mysterious gas giants and ...

Discovery of 2017OF201, a large trans-Neptune Object, challenges previous beliefs about the Kuiper Belt and hints at the existence of a theoretical Planet Nine.

Astronomers find evidence of a possible ninth planet beyond Neptune, reigniting the debate about the formation of the Solar ...

The chance of a planet forming in the outer reaches of the solar system - a hypothetical Planet Nine - could be as high as 40 ...

The presence of another planet in the solar system could explain the odd movements of some of the bodies in the Kuiper Belt.

That will allow the observatory to detect anything that changes — like, say, Planet Nine moving across the sky. Sponsor Message "If it's there, we should be able to find it, pretty easily," says ...

An elusive Earth-like planet in our solar system could finally be discovered within the next few years. Known as Planet Nine or Planet X, it is a hypothetical planet that has long been rumoured to ...