IAU definition of planet who had theorized on the existence of the large trans-Neptunian object Planet X, and Tombaugh been searching for Planet X when he found Pluto. Almost immediately after its discovery, however, astronomers questioned whether Pluto could be Planet X. Willy Ley wrote a column in 1956 titled "The Demotion of Pluto", stating that it "simply failed to live up to the advance publicity it received as 'Planet X' before its discovery. It has been a disappointment all along, for it did not turn out to be what one could reasonably have expected". In 1978, Pluto's moon Charon was discovered. By measuring
Tombaugh Regio the International Astronomical Union (IAU), together with names for 13 other surface features on Pluto. Some people find the feature also resembles the Disney character Pluto, an animated non-anthropomorphic dog which shares the name of the dwarf planet. The Walt Disney Company acknowledged this perceived likeness in a short animation. Tombaugh Regio Tombaugh Regio (), nicknamed The Heart after its shape, is the largest bright surface feature of the dwarf planet Pluto. It is just north of the equator, to the northeast of Cthulhu Macula and to the northwest of Krun Macula, which are both dark features. Its western lobe,