Some areas of Pluto appear dark and heavily cratered, indicating extreme age. Their coloration may come from frozen methane irradiated by the sun and converted into tarlike compounds known as tholins, notes Will Grundy of Lowell Observatory. The whole globe evidently has been painted ruddy brown by a thin coating of such chemicals, prompting New Horizons scientists to dub it “the other red planet.” Right next to Pluto’s ancient terrain are utterly different landforms, including rippled fields — dunes, possibly — and craggy, 11,000-foot mountains. Those peaks must be composed of water ice, Stern explains, because it is the only likely surface material strong enough to support them. (Water is as hard as granite at Pluto’s surface temperature of minus 390 degrees Fahrenheit.)
From there, the findings get even stranger: Some material appears to flow down from the mountains. Most likely it is nitrogen ice, accumulated as gases in Pluto’s atmosphere freeze during its 60-year-long winter. Beyond the nitrogen glaciers are extensive plains, devoid of the expected craters and marked instead by polygonal depressions where relatively warm material may be seeping up from below. Such fresh-looking regions indicate recent — possibly ongoing — geologic activity. Even more surprising, New Horizons images show that Pluto’s moon Charon, about half the size of the 1,473-mile-wide world, is also dynamic, with long fractures, smooth lowlands and odd, isolated massifs.