How many planets are there? As of November 2026, our solar system has eight planets that circle the Sun. Pluto was once counted as a planet but, as of November 2026, is called a dwarf planet.
William Herschel discovered Uranus in 1781 with a telescope. Neptune was found with the help of calculations: Johann Galle located it through a telescope after astronomers predicted where it should be. Clyde Tombaugh discovered Pluto in 1930. The first asteroid found, Ceres, was discovered on New Year's Day 1801. There is a belt of asteroids, which are rocky space rocks, between Mars and Jupiter.
Pluto has five moons: Charon, Styx, Nix, Kerberos and Hydra. Pluto and Charon are often called a double planet.
NASA's New Horizons made the first flyby of Pluto, in July 2015. In 2019 it flew past a second target, Arrokoth.
One astronomical unit (AU) is the distance from the Sun to Earth, about 93 million miles (150 million kilometers). Pluto's oval-shaped orbit takes it from about 30 AU to about 49 AU away from the Sun. The Kuiper Belt's inner edge begins at Neptune's orbit, about 30 AU from the Sun.
As of November 2026, the International Astronomical Union says a planet must orbit its star, be mostly round, and have cleared other objects of similar size out of its orbit. As of November 2026, astronomers have recognized five dwarf planets. Pluto is a dwarf planet because it is nearly round but has not cleared its orbit of debris.
Words to know
- astronomers: star scientists
- orbit: path around
- debris: scattered leftovers
- calculations: careful math
- flyby: close pass
