Intermediate 
For 85 years, it was just a grey blob on classroom maps of the solar system. But, on 15 July, Pluto was seen in high resolution for the first time. The images show dramatic mountain ranges made from solid water ice as big as the Alps or the Rockies.
The extraordinary images of the former ninth planet and its large moon, Charon, were sent back 4bn miles to Earth from the New Horizons spacecraft. They are the climax of a mission that has been quietly underway for nearly ten years.
Alan Stern, the missions principal investigator, said New Horizons is returning amazing results. The data look absolutely gorgeous, and Pluto and Charon are just mind-blowing.
One of the biggest surprises was the discovery that there are mountains in the Kuiper belt, the solar systems mysterious third zone where Pluto is, with about 100,000 smaller icy objects. John Spencer, a mission scientist, said the mountains appear to be around 3,000 metres high and several hundred miles across.
The detailed image of one edge of the dwarf planet showed not a single crater. This tells scientists that there has been recent geological activity on the surface, which could include dramatic geysers throwing ice into the atmosphere or cryo-volcanoes that erupt in explosions of ice.
Pluto used to be the ninth planet but, since 2006, it has been known as a dwarf planet. The NASA press conference began with spectacular images of the sun and the eight official planets. Weve 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 shown.
Stern said that there would be many more images and that we would learn a lot more about the planet during the coming year. The images have already produced some surprises. Scientists believe the mountains are made from water ice with just a thin cover of exotic ices, methane and nitrogen.
Water ice is strong enough to hold up big mountains and thats what we think we can see here. This is the first time weve seen this. The methane and nitrogen are just a coating. The mountains on Pluto probably formed no more than 100m years ago  extremely recently in the 4.56bn-year-old solar system. This suggests the region, which covers about 1% of Plutos surface, may still be geologically active. The images are the first to show ice mountains, except those found on the moons of giant planets.
The images are so detailed that, if the craft were flying over London, we would be able to see the runways at Heathrow airport.
The distance to Pluto  5bn km  means it takes New Horizons hours to send back a picture and it will take 16 months to send back all the data. The team also announced that the heart-shaped feature visible on Pluto will now be known as the Tombaugh Regio, after Clyde Tombaugh, who discovered the dwarf planet in 1930.
The new view of Charon reveals an area of cliffs stretching about 1,000km. This suggests cracks in Charons surface, which could also be the result of geological activity. The image also shows a dramatic canyon about 7 to 9km deep.
Cathy Olkin, a mission scientist, said: Charon just blew our socks off when we saw the new image today. The team has just been abuzz. There is so much interesting science in this one image alone. Scientists think that Pluto is two thirds rock surrounded by a lot of ice, with surface temperatures of about minus 230C. As the 460m mission continues into the Kuiper belt, scientists hope that it will help us to see and understand more of the ancient solar system and the origins of planets. It may even help to explain the formation of the Earth itself.
Andrew Coates, head of planetary science at the Mullard Space Science Laboratory, said: These Kuiper belt objects are the building blocks of the outer solar system. Theyre all very cold  its like a cosmic deep freeze. Its the best way of preserving solar system history. That is what is so fascinating about this. Its a really thrilling time for solar system exploration.
In August 2015, mission scientists will choose which of two objects to visit next. NASA estimates that the spacecraft will be able to keep recording and sending back data until the mid-2030s. Then, its plutonium power source will run out and it will drift outwards towards the edge of the solar system and deep space.
New Horizons also observed the smaller members of the Pluto system, which includes four other moons: Nix, Hydra, Styx and Kerberos. New Horizons is a true mission of exploration, showing us why basic scientific research is so important, said John Grunsfeld, associate administrator for NASAs Science Mission Directorate.
The images also suggest that Hydras surface is probably coated with water ice. Future images will reveal more clues about the formation of this, and the other moon, billions of years ago.