As astronomers track down more clues as to the existence of a large world orbiting the sun in the outer fringes of the solar system, a classic planetary purveyor of doom has been resurrected as a possible trigger behind mass extinctions on Earth.

Yes, I’m talking about “Planet X.” And yes, there’s going to be hype.

Before we dive into comet impacts, extinctions and possible exciting planet discoveries, let’s look at the dramatic history of Planet X.

"Could 'Planet X' cause comet catastrophes on Earth?" Or, should that headline be "Has 'Planet X' caused comet catastrophes on Earth?" To read more, click here.