For more than 5,000 years it was generally accepted that there were just five planets (in addition to the Earth) circling the Sun. There had been some suggestions of another planet waiting to be found between the orbits of Mars and Jupiter, but no one seems to have thought of any worlds lurking beyond Saturn. Imagine the impact on the scientific world of the chance discovery of a seventh planet by an amateur astronomer.
KeywordsClose Approach Giant Planet Hubble Space Telescope Impact Crater Outer Solar System
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