Assertion: planet's history | /r/CapableOf | end 25-year-long search
Facets:
Source sentences:
text: History of Discovery Pluto was discovered in 1930 by the then amateur astronomer Clyde Tombaugh at Lowell Observatory in Arizona, USA , ending a 25-year-long search for what had become known as 'Planet X' - a sizeable planet beyond Neptune which was thought to be having a significant gravitational effect on the orbits of Uranus and Neptune.