It wasn't discovered to not be a planet, it was decided to no longer be a planet. Recently, the last 2 or 3 years scientist decided (not all) it was not an official planet.
pluto was discovered in 1930
Pluto was a planet discovered in 1930
Pluto was discovered in 1930 and assumed to be a planet at that time.
Pluto, Discovered in 1930
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Pluto the 10th planet was discovered
The dwarf planet Pluto was discovered in the year 1930. It was discovered by Clyde Tombaugh and is the largest object found in the Kuiper belt.
An American astronomer named Clyde Tombaugh discovered Pluto in 1930