Discovery of Pluto. Plates from which US astronomer Clyde Tombaugh (1906-1997) made the discovery of the minor planet Pluto. Tombaugh was an assistant at the Lowell Observatory. It was Lowell himself who predicted the existence of a ninth planet, set up a team to find it. Tombaugh invented the blink comparator to facilitate the search. This device allowed the comparison of two photographs of the sky, which showed if any object had altered position. After 7000 hours of work, he found a tiny object (marked by arrows) outside the orbit of Neptune, which was named Pluto.