Mars had an oxygen-rich atmosphere around 4 billion years ago
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A comet's tail always points away from the sun.
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An organisation called Mars One is planning to establish a permanent colony of humans on Mars by 2023.
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On Titan, Saturn's largest moon, the atmosphere is so thick and the gravity so low that humans could fly through it by flapping "wings" attached to their arms.
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The Sun and Moon appear to be the same size because the moon is 400 times smaller than the Sun, but 400 times closer to Earth.
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Jupiter is bigger than all the other planets combined.
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There's a mysterious dwarf planet between Mars and Jupiter called 'Ceres' which has never been visited by spacecraft or photographed in detail, however, Earth-bound telescopes reveal a large bright shining spot on the surface of this planet, the origin and nature of which are unknown.
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