alone.” Pluto is thought to be composed of about two thirds rock encased in a lot of ice, with surface temperatures of about minus 230C. As the £460m mission travels onwards into the Kuiper belt, scientists hope that it will open up a window on the ancient solar system and the origins of planets, potentially helping 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. They’re all very cold – it’s like a cosmic deep freeze. It’s the best way of preserving solar system history. That is what is so fascinating about this. It’s 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 transmitting until the mid-2030s. Then, its plutonium power source will run out and it will shut down, drifting outwards towards the edge of the solar system and deep space beyond. New Horizons also observed the smaller members of the Pluto system, which includes four other moons: Nix, Hydra, Styx and Kerberos. A new sneak-peek image of Hydra is the first to reveal its apparent irregular shape and its size, estimated to be about 43 by 33km. “New Horizons is a true mission of