No one likes being kicked out of a tight-knit group, but you can't really blame the International Astronomical Union (IAU) for downgrading Pluto to "dwarf planet" in 2006. The fact is, planets get to be planets because of their size, and Pluto isn't even the largest object in the Kuiper Belt – the region of the outer solar system beyond Neptune.
Pluto is 1,430 miles (2,370 km) across, which makes it smaller than our Moon. Its diameter is only 18% of Earth's, and it has less than 1% of our planet's volume. To put Pluto's relatively unimpressive size into perspective, its surface area is roughly the same as Russia. And although Russia is the world's largest country, that certainly doesn't grant it planet status. In fact, Pluto's diameter is less than Russia's east-west width and north-south height.
Basically, Pluto only retained its planetary status for so many decades because we didn't have the telescopic power to see much that far away. Once other objects were discovered nearby that rivaled Pluto, its planet title was pretty well sunk.
- The ashes of Clyde Tombaugh, the American astronomer who discovered Pluto in 1930, were aboard the New Horizons spacecraft that passed by Pluto in 2015.
- An 11-year-old girl named Venetia Burney first suggested the name Pluto; it was deemed fitting because the former planet, like the Roman god of the underworld, is so far away from others.
- Pluto, the famous dog from Walt Disney, debuted in the same year Pluto was discovered and is named after the one-time planet.