Growing up, I was taught that there were nine planets in the solar system. That all changed in 2006, when the International Astronomical Union voted to demote Pluto's status to that of dwarf planet.

For about a decade, he and other researchers have been trying to prove that the so-called "Planet 9" exists. So far, the only evidence has come from some oddities in the orbits of small Pluto-like ...

A powerful new observatory is the best hope yet for finding the elusive Planet 9, a large planet that some scientists say is hidden in our solar system.

For about a decade, he and other researchers have been trying to prove that the so-called "Planet 9" exists. So far, the only evidence has come from some oddities in the orbits of small Pluto-like ...