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
Makemake Makemake Makemake (minor-planet designation 136472 Makemake) is a dwarf planet and perhaps the largest Kuiper belt object in the classical population, with a diameter approximately two-thirds that of Pluto. Makemake has one known satellite, S/2015 (136472) 1. Makemake's extremely low average temperature, about , means its surface is covered with methane, ethane, and possibly nitrogen ices. Makemake was discovered on March 31, 2005, by a team led by Michael E. Brown, and announced on July 29, 2005. Initially, it was known as and later given the minor-planet number 136472. Makemake was recognized as a dwarf planet by the International Astronomical