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Ancient civilisations thought comets were gods. They believed them to be bringers of life or harbingers of doom - strange, magical, mysterious things that moved through the sky, fiery streaks of light that tore across the heavens.

Isaac Newton was the first to make sense of comets and to him they were the key to unlocking the secrets of gravity - nothing to do with an apple. Hundreds of years later, a new breed of space missions are visiting comets, travelling millions of miles to touch down on these tiny balls of rock flying through space at 20,000 mph. The spectacular images we now have are showing us what comets are really made of, where they come from, and their often surprising influence on events on Earth.

What they reveal is that our ancestors may have been right all along and that comets and meteors really are like gods, or at least they can exert tremendous influence over our world. They have brought terrible destruction to the Earth and may one day do so again. But they also may have brought life itself to the planet.