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

For the dwarf planet candidate, one trip around the sun takes over 24,000 years. Its orbit challenges a proposed path for a hypothetical Planet Nine.

Jupiter, roughly 562 million miles from Earth today, has nearly 100 moons. But Batygin and his collaborator Fred Adams' ...

"How planets are born is an unsolved area of research," astrophysicist Daniel Price of Australia's Monash University told Newsweek.

Today, it’s believed that Jupiter and Saturn, the largest planets, were the first to fully form, both within a few million ...

A new dwarf planet, discovered beyond Neptune and described as Pluto's 'cousin,' could void the hypothesis of a Planet X in ...

The outer solar system is a vast and mysterious place that could be harboring hidden objects we know almost nothing about — from the elusive Planet Nine and baby black holes to interstellar ...