08/25/2026
Twenty years ago today, Pluto was demoted to a dwarf planet. Discovered in 1930, it was considered to be the ninth planet in our solar system until 2006, when the International Astronomical Union (IAU) voted to reclassify it. In order to qualify as a planet, Pluto must orbit the Sun, be nearly round, and clear its orbit. While Pluto orbits the Sun and is round, it’s not massive enough to control any other object in its orbit with its gravitational force.
Pluto also consists of a rocky core with ice around the outside—making it more similar to objects in the Kuiper Belt, a band of cometary debris at the edge of our solar system, than it is to the other eight planets. Located 3.7 billion mi (5.9 billion km) from the Sun, it takes Pluto 248 Earth years to orbit the Sun.
Image: NASA, PD, Wikimedia Commons
