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Neptune resembles Uranus, without the rings, and is a bluish-green in colour. Its atmosphere is made up of methane, hydrogen and helium. It has a diameter of around 49 400 km and a surface temperature of -218° C. It takes Neptune almost 165 years to orbit the sun, and so, since its discovery in 1846, it has not made a complete revolution. It rotates once on its axis every 16 hours. Neptune has some six satellites, with Triton and Nereid being most well known. | |