Pluto is indeed a weird planet. According to the scientific analysis of data and photo from the New Horizons mission July flyby, Pluto is home to "floating hills", some rock-hard glaciers made of frozen water.
According to NASA, these water ice glaciers float around on frozen nitrogen. On the frigid dwarf planet nitrogen is much more common than water. Water ice glaciers on Pluto are likely as hard as Earth's mountains made of rock because of the average temperature of minus-380 degrees Fahrenheit. Because nitrogen freezes when it hits minus-346 degrees, on Pluto it is icy but flowing.
That water ice is less dense than frozen nitrogen and for this reason NASA scientists believe that when the water ice hills break apart they are carried atop the nitrogen flows. The isolated hills may be composed of fragments of water ice from the surrounding uplands. Based on the nitrogen flow pattern, the water ice hills move in chains and cluster together.
According to the website Phys.org, data and images from NASA's New Horizons mission show individual hills that measure one to several miles across. For example, the hill informally named Challenger Colles is 22 miles by 37 miles across.
Most of the hills are located within Pluto's "heart", in the vast ice plain informally named Sputnik Planum. They are likely miniature versions of the larger mountains found on the western border of the Sputnik Planum. These "floating hills" are yet another example of the abundant geological activity present on the dwarf planet. In some areas of Sputnik Planum, the water ice clusters span 12 miles across. They move over time on the frozen nitrogen sea like icebergs in Earth's Arctic Ocean.
Along the flow paths of the glaciers are formed "chains" of drifting hills. They become subject to the convective motions of the nitrogen ice and are pushed to the edges of the cells when they enter the cellular terrain of central Sputnik Planum.
