Pluto's mysterious, floating hills

Hills of water ice on the dwarf planet believed to be floating in a sea of frozen nitrogen like icebergs in Earth's Arctic Ocean

The nitrogen ice glaciers on Pluto appear to carry an intriguing cargo: numerous, isolated hills that may be fragments of water ice from the dwarf planet's surrounding uplands.
These hills individually measure one to several miles across, according to images and data from Nasa's New Horizons mission.
Because water ice is less dense than nitrogen-dominated ice, scientists believe these water ice hills are floating in a sea of frozen nitrogen and move over time like icebergs in Earth’s Arctic Ocean.
The hills are likely fragments of the rugged uplands that have broken away and are being carried by the nitrogen glaciers into Sputnik Planum, the informal name for the vast ice plain within Pluto's 'heart'.


http://www.telegraph.co.uk/news/science/space/12141613/Plutos-mysterious-floating-hills.html