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. The planets Mercury, Venus. Mars, Jupiter, and Saturn were all known since antiquity. Then Sir William Herschel discovered Uranus in 1781, and 65 years later, in 1846, Johann Calle and Urbain le Verner discovered Neptune. Variations in orbital perturbations of the planets and theoretical astronomy were responsible for predicting and discovering the three outermost planets (Uranus, Neptune, and Pluto) and so Pluto's story is also, to some extent, the story of its planetary neighbors. What kind of world is Pluto? Much is still a mystery (its