An adventure in scientific discovery Pluto, the farthermost planet in the solar system, some 3,673 million mites from the Sun, was discovered by Clyde Tombaugh at the Lowell Observatory in 1930. The fiftieth anniversary of Pluto's discovery will be celebrated in 1980 and OUT OF THE DARKNESS: THE PLANET PLUTO tells the exciting scientific story of the twenty-five year search for a planet X beyond Neptune, and its discovery-the only planet found in the twentieth century.