The Sun may have started out life with a companion—and that may have big implications for the mysterious "Planet 9".

New discoveries of objects in the Kuiper Belt have also presented challenges for the Planet Nine theory. The latest is known ...

In 2016, a pair of astronomers made an exciting announcement: There might be a hidden planet about ten times the size of Earth lurking somewhere in the most distant part of our solar system ...

A new minor planet called "the Goblin" is the second most distant known object in the solar system ...

After a decade-long search, some scientists say a growing number of clues point to the existence of a hidden planet in the Kuiper Belt beyond Neptune — and they may soon have the opportunity to ...

Scientists have found evidence of a true ninth planet in our solar system. Nicknamed "Planet Nine," the real-life Planet X appears to have the mass of 10 Earths and is 20 times farther from the ...

Planet 9 may be closer and easier to find than thought—if it exists A new study's "treasure map" suggests that a planet several times more massive than Earth could be hiding in our solar system ...

That would actually be evidence against Planet Nine, instead we got this beautiful agreement of the theory. AM: Has this new data helped with your search for Planet Nine?

Discover the order of planets in the solar system. From Mercury to Neptune, explore our solar system and learn more about our cosmic home.

Nine Planets, or Eight? Probing Pluto's place in the solar system By Ron Cowen June 5, 2001 at 10:58 am - More than 2 years ago Any fourth grader knows the names of the solar system’s planets.