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The New Horizons science team has released a new image of Pluto’s smooth heart-shaped area, dubbed Sputnik Planum, focusing this time on the mountains of water ice that pop up through the plain and are apparently floating on the nitrogen sea, having broken off from the shoreline.
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. ‘Chains’ of the drifting hills are formed along the flow paths of the glaciers. When the hills enter the cellular terrain of central Sputnik Planum, they become subject to the convective motions of the nitrogen ice, and are pushed to the edges of the cells, where the hills cluster in groups reaching up to 12 miles (20 kilometers) across.
I have significantly cropped the image to show it here. Be sure and check out the full version, because there is a wealth of fascinating details in it.