NASA’s New Horizons mission does it again – apparently Pluto has “floating hills”. February 4, 2016 NASA released images captured by New Horizons, 12 minutes before closest approach to Pluto on July 14, 2015, at a distance of 16,000 kilometers.
Abundant hills measuring a few kilometers across, are thought to be “water ice”, floating on glaciers of dense nitrogen ice –
… likely miniature versions of the larger, jumbled mountains on Sputnik Planum’s western border. They are yet another example of Pluto’s fascinating and abundant geological activity.
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 …
View larger. | Hills of water ice on Pluto ‘float’ in a sea of frozen nitrogen. They’re thought to move slowly over time, somewhat like icebergs in Earth’s Arctic Ocean. For the scale here, notice the feature informally named Challenger Colles – honoring the crew of the lost Space Shuttle Challenger. It appears to be an especially large accumulation of these hills, measuring 37 by 22 miles (60 by 35 km). Image via NASA/JHUAPL/SwRI.