Scientist have spotted hills made of ice floating in a sea of frozen nitrogen in Pluto's "heart," one of the dwarf planet’s must distinct regions because of its shape."Bobbing" seems rather misleading to me. Moving very slowly as frozen nitrogen moves about it not really "bobbing" as we see it. However, for a creature from Pluto, it might seem a lot quicker, seeing that the temperature is a balmy -220 C (-380 F), and living things don't move very fast at those temperatures, unless they're composed largely of liquid hydrogen or helium, the way terrestrial life is largely composed of water.
NASA reports that the isolated hills may be fragments of water ice from the surrounding uplands. They’re spread across a vast plain of nitrogen-dominated ice known as Sputnik Planum, the heart’s western lobe, and are likely broken fragments of the mountains found on its far western edge.
What enables the hills to float is a simple matter of chemistry: water ice is less dense than nitrogen ice. A blog post on NASA’s website describes the hills as moving “like icebergs in Earth’s Arctic Ocean.”
“They are yet another example of Pluto’s fascinating and abundant geological activity,” it says.My guess is that the "mysterious" internal heat source is simply radioactive decay, the same as it is for the earth.
Scientists hypothesize that nitrogen glaciers carried the hills into Sputnik Planum after they broke away from the rugged uplands. A newly released image show chains of the drifting hills along the flow paths of the glaciers, where they’ve formed clusters that reach up to 12 miles across.
At the northern end of the image, a feature informally named Challenger Colles – honoring the seven astronauts who died in the space shuttle Challenger explosion in 1986 – appears to be an especially large accumulation of these hills, measuring 814 square miles.
The center of Sputnik Planum features massive polygonal blocks of nitrogen ice. Scientists say thermal-convection processes, which in turn are driven by Pluto’s mysterious internal heat, probably produced these distinctive cell-like structures.