Is there a massive undiscovered planet on the outer reaches of the solar system? The idea has been around since before the ...

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

We still don't know for sure if there's a ninth planet in our solar system, but a new discovery could help to prove that ...

A newly discovered dwarf planet called 'Ammonite' (2023 KQ14) has been spotted in the outer solar system, and it could be ...

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

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

Planet Nine's composition is probably "most like Neptune," due to its distance from the sun, Brown said. "That would put its diameter at something like two times the width of Earth," he added.

If Planet 9 is real, this observatory has around a 70 to 80 percent chance of finding it, he estimates, adding that it's not a sure thing because there are so many uncertainties.