in explosions of ice rather than molten rock. In a nod to Pluto’s former status as the ninth planet, until it was downgraded to a dwarf planet in 2006, the NASA press conference began with a rundown of spectacular images of the sun and the eight official planets. “We’ve brought what was previously a blurred point of light into focus,” said Dwayne Brown, NASA spokesman, as scientists and journalists waited for the image to be unveiled. Stern described the images as “just skimming the surface” of what would be learnt about the planet during the coming year. They have already produced some surprises. Scientists believe the mountains are made from water ice with just a thin veneer of “exotic” ices, methane and nitrogen. “You can’t make mountains out of methane and nitrogen,” said Spencer. “Water ice is strong enough to hold up big mountains and that’s what we think we’re seeing here. This is the first time we’ve seen this. The methane and nitrogen are just a coating.” The mountains on Pluto are likely to have formed no more than 100m years ago – extremely recently given the 4.56bn-year-old solar system. This suggests the close-up region, which covers about 1% of Pluto’s surface, may still be geologically active. The images are the first to show ice mountains outside of the moons of giant planets and raises the question of what kind of