Two professors at the California Institute of Technology laid out an argument for the existence of a planet perhaps 4,500 times the mass of Pluto.

Source: Ninth Planet May Exist Beyond Pluto, Scientists Report

We grew up with nine planets, then Pluto got demoted, and now there may be nine again? Something to pay attention to if you’ve got a budding astronomer at home!

Also, according to the New York Times, the old mnemonic for remembering the planets in order was My Very Educated Mother Just Served Us Nine Pizzas. I can’t remember what I learned in elementary school, but I’m pretty sure that wasn’t it. Anyone else remember learning one that didn’t involve pizzas?