Shortest time from discovery to its exploration by spacecraft for a planet/dwarf planet

Pluto, discovered on 18 February 1930 by Clyde Tombaugh (USA), was first explored by spacecraft on 14 July 2015 – a total of 31,193 days later.

Clyde Tombaugh discovered Pluto by comparing photographic plates of the same parts of the sky taken over a period of time. This meant that anything moving in a slow orbit around the Sun would appear to jump from one spot to another, when examining pairs of plates. Tombaugh used a device called a blink comparator to spot Pluto moving against the background of stars.

In 14 years of searching for planets, Tombaugh studied 90 million images of stars.