Pic: Science Alert Neptune and Uranus are the two planets farthest from the Sun. Like Jupiter and Saturn, they are composed mostly of gas. These two planets are sometimes known as ice giants because they contain a large amount of icy water, methane and ammonia. What colour is Neptune? Neptune appears greeny-blue because of the methane gas in its atmosphere. This gas absorbs red light in the spectrum, making it seem that Neptune is a vivid, azure blue-green. The same effect can be seen with Uranus, which also has a lot of methane in its atmosphere, although that planet appears to be a much paler shade of turquoise blue. How long is a year on Neptune? Neptune is so far from the Sun - over 4500 million kilometres – that its orbit takes about 165 Earth years. So one year on Neptune lasts for 165 Earth years. 'Neptune has 17 times the mass of Earth and is slightly heavier than its similar sister planet, Uranus, which is only 15 times heavier.' Who discovered Neptune? Two mathematici
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