NASA's New Horizons missions collected images and data indicating the isolated hills on Pluto may be fragments of water ice from the planet's surrounding uplands. The hills are thought to float in a sea of frozen nitrogen and move just like the icebergs in Earth's Arctic Ocean.
Numerous, isolated hills on the Pluto's surface, located in the Sputnik Planum plain, are most likely smaller versions of the larger mountains found on the plain's western border. They spread between one and several kilometers across.
The water ice hills have likely broken away from the rugged uplands and are being carried into Sputnik Planum by the nitrogen glaciers due to their lower density values. As the hills enter the cellular terrain of central Sputnik Planum, they become influenced by the nitrogen ice convective motions and are being pushed to the edges of the cells. There, they cluster in 20 km (12 miles) wide groups.
Hills of water ice on Pluto ‘float’ in a sea of frozen nitrogen and move over time like icebergs in Earth’s Arctic Ocean. Image credit: NASA/JHUAPL/SwRI
The image obtained by the New Horizons shows the inset in context next to a larger view that covers most of Pluto's encounter hemisphere. The image resolution is approximately 320 m (1 050 feet) long and 340 km (210 miles) wide, obtained in a range of about 16 000 km (9 950 miles) from Pluto, 12 minutes before New Horizons' closest approach to the planet on July 14, 2015.
At the northern end of the image is the Challenger Colles feature, which appears to be a particularly large accumulation of these hills, occupying an area of 60 x 35 km (37 x 22 miles). The feature is located away from the cellular terrain, near the boundary with uplands. According to experts, this could be a place where hills have been 'beached' due to the nitrogen ice being exceptionally shallow.
Featured image: Hills of water ice on Pluto ‘float’ in a sea of frozen nitrogen and move over time like icebergs in Earth’s Arctic Ocean. Image credit: NASA/JHUAPL/SwRI