The space agency analysed data and imagery of the planet's surface and found a range which is apparently covered with methane ice.
The US space agency have released the most detailed pictures yet of the rough and varied terrain of the distant dwarf planet
New close-up images of Pluto have been released by NASA.
Nasa's New Horizons spacecraft is just hours away from flying past the last unexplored world in our Solar System.
Nasa's New Horizons spacecraft has captured a stunning image of Pluto ahead of its historic flyby next week.
Pluto's four moons and two central bodies are locked in an intricate and uneven dance - due to complex gravitational fields.
Astronomers have launched a competition to name Pluto's two tiniest moons. The moons, discovered over the past two years, are currently known as P4 and P5.
Three of the moons already have names associated with Hades and the underworld. They are Charon, the ferryman of Hades, as well as Nix, the night goddess and the multi-headed monster Hydra.
Online voting will last two weeks. Twelve choices are available at the website 'Pluto Rocks'. Choices include the hero who slew Hydra, Hercules and Styx, the river to the underworld.
Write-in suggestions are welcomed.
To vote online, visit Pluto Rocks here.