Since the discovery of the outermost planet Pluto, in 1930, astronomers have wondered whether another planet might exist unseen in the outer darkness. They have looked, but nothing has been found. Clyde Tombaugh, the man who discovered Pluto, photographed the entire sky in search of extra planets. He concluded that if any other planets existed they must either be very small, or very far away. Most astronomers think that the solar system ends with Pluto.
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