Pluto

   Pluto was discovered by Clyde W. Tombaugh on February 18, 1930.Once found, Pluto's faintness and lack of a resolvable disc cast doubt on the idea that it was Lowell's Planet X. Estimates of Pluto's mass were revised downward throughout the 20th century.
                 
     Images of  Clyde W. Tombaugh

 About Pluto     

Image of Pluto

   Pluto has a moon which is almost the size of Pluto itself. It is the largest object in the Kuiper belt, the tenth-most-massive known body directly orbiting the Sun, and the second-most-massive known dwarf planet, after Eris. Like other Kuiper belt objects, Pluto is primarily made of rock and ice, and is relatively small, about ¹⁄₆ the mass of the Moon and ¹⁄₃ its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the Sun. Hence Pluto periodically comes closer to the Sun than Neptune, but an orbital resonance with Neptune prevents the bodies from colliding. In 2014 it was 32.6 AU from the Sun. Light from the Sun takes about 5.5 hours to reach Pluto at its average distance (39.4 AU).

     The first colour image taken by
 Charon made by new horizons