If you want to keep track of the order, there is a simple trick for remembering it. You may be thinking, "Wait a minute, I thought there were a total of nine planets!" ...

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. Now, a team of astronomers may have ...

When most of us left school there were still 9 planets – but we’ve come a long way since Pluto’s demotion. Here’s what’s next on the space agenda.

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.

Our solar system used to have nine planets. Astronomer Mike Brown, also known as “the man who killed Pluto,” said he got hate mail from kids and obscene calls at 3 a.m. for years after his ...

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.