Pluto just keeps getting weirder. NASA released new images last week of what the space agency described as "floating hills," essentially massive icebergs drifting in a sea of frozen nitrogen. These hills, which can be several miles across, are located in the middle of the Sputnik Planum, or the icy plains of the planet's heart-shaped region: The region is home to glaciers as well as clusters of these frozen hills, which NASA said could be fragments of water ice from the nearby uplands.