Percival Lowell launches a search for "Planet X." His calculations are based on inaccurate contemporary estimates of Uranus' mass, but his quest will eventually turn up a different world.
(Credit: Lowell Observatory)
Lowell Observatory
Clyde Tombaugh discovers Pluto from Lowell Observatory in Arizona by seeing it move on photographic plates over a six-day period.
(Credit: Lowell Observatory)
Lowell Observatory
Gerard Kuiper and others propose the existence of a large belt of icy objects beyond Neptune.
(Credit: Lunar and Planetary Laboratory)
Lunar and Planetary Laboratory
Dale Cruikshank, Carl Pilcher, and David Morrison discover methane ice on Pluto, providing the first indication that the planet's surface is icy rather than rocky.
James Christy and Robert Harrington discover Pluto's largest moon, Charon. It appears as a slight elongation in these images of Pluto.
(Credit: U.S. Navel Observatory)
U.S. Navel Observatory
A series of mutual occultations between Pluto and Charon begins, allowing scientists to ...
