Planet Nine should appear stationary over the course of a single day but show detectable movement over months.

"It is possible that a planet once existed in the solar system but was later ejected, causing the unusual orbits we see today ...

Researchers use the Subaru Telescope in Hawaii to find a small object on the outer edge of the Solar System. Nicknamed ...

Astronomers have hoped for the existence of Planet Nine for years. Things were looking promising, but this discovery might ...

A telescope has discovered a new world on the edge of the Milky Way – potentially confirming the ‘Planet X’ theory. Beyond ...

Ammonite was discovered using the Subaru Telescope in Hawaii, with follow-up confirmation from the Canada-France-Hawaii ...

The discovery was made by astronomers using the Subaru Telescope, which is situated atop a dormant volcano in Hawaii.

Computer simulations show that planets could be flung out of the inner solar system, supporting the possible existence of a "Planet Nine" or "Planet X" beyond Neptune.

Only eight planets call our solar system home. Or there might still be nine if some astronomers are correct about an as-yet undiscovered large body out past Neptune.

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

For years, scientists have puzzled over how these “wide-orbit” planets, including the elusive Planet Nine theorized in our own solar system, could have formed.

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.