For the better part of a century, we believed there were nine planets in our solar system, with Pluto being the farthest from the sun. Since the discovery of more Pluto-sized dwarf planets, that ...

At just 23 years old, Tombaugh sent his drawings ... planet with mountains, valleys and a now-iconic heart-shaped feature known as Tombaugh Regio. "New Horizons essentially turned Pluto from ...

Pluto — famous for being reclassified as a dwarf planet — might not have a heart of ice after all. In fact, every bit of Pluto was assumed to be frozen over considering its distance from the Sun.