Dwarf Planets: Pluto, Ceres and Their Neighbors
Round, small and still sharing their orbits with other bodies: the worlds between planets and asteroids.
A dwarf planet is a world that orbits the Sun, is massive enough for its own gravity to pull it into a rounded shape, and has not cleared other objects out of its orbital neighborhood. It is not a moon. The International Astronomical Union (IAU) wrote those rules in 2006, and they explain most of what this category holds.
The IAU recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake and Eris. Ceres lives in the asteroid belt between Mars and Jupiter and is about 940 km (584 miles) across. The other four orbit beyond Neptune, in the icy outskirts of the Solar System. Many more distant bodies are candidates, and astronomers keep measuring them to see whether they qualify.
Two NASA spacecraft turned this field from a list of faint dots into a set of real places. Dawn orbited Ceres from 2015 to 2018 and mapped its bright salt deposits. New Horizons flew past Pluto in July 2015 and found mountains of water ice, glaciers of nitrogen and a thin, hazy atmosphere. Nothing has visited Eris, Haumea or Makemake yet. What we know about them comes from telescopes, from starlight that blinks out as they pass in front of stars, and from careful math.
The nine guides below start with the definition and the Pluto decision, then take each dwarf planet in turn: what it looks like, how it spins, which moons it has and how it was found. Where a number can change with new measurements, the guide says when it was checked and which agency page it came from.
If you are new to the topic, read what a dwarf planet is first. If you want the story behind the headlines, go to why Pluto is a dwarf planet.
The nine guides
What Is a Dwarf Planet? The IAU Definition Explained
The three tests behind the label, the extra rule about moons, and how dwarf planets compare with planets, asteroids and satellites.
How Many Dwarf Planets Are There?
Five names are official as of November 2026. Here is who is on the list, who might join it, and why astronomers give different totals.
Why Pluto Is a Dwarf Planet
Pluto is not too small to be a planet. It failed one specific test. Here is the 2006 vote, the rule behind it and the arguments that continue.
What New Horizons Found at Pluto
The 2015 flyby showed a Pluto with glaciers, mountains, dunes and layered haze. This guide sorts the main findings and what is still uncertain.
Charon and Pluto's Four Small Moons
Pluto has five known moons as of November 2026. See how Charon stacks up against Pluto and why the four small moons tumble instead of spinning steadily.
Ceres: The Dwarf Planet in the Asteroid Belt
Ceres holds about a quarter of the belt's mass. Learn why it counts as an asteroid and a dwarf planet, and what Dawn found there from 2015 to 2018.
Eris: The Dwarf Planet That Reopened the Debate
Found in old images and announced in 2005, Eris forced a vote on what a planet is. Here is its story, its moon Dysnomia and how it measures up to Pluto.
Haumea: The Fast-Spinning, Egg-Shaped Dwarf Planet
A day on Haumea lasts under four hours. See how that spin shaped it, how a 2017 occultation revealed a ring and why astronomers still argue about its discovery.
Makemake: A Bright, Frozen World Beyond Neptune
Makemake is the second-brightest Kuiper Belt object seen from Earth. This guide covers its discovery, surface, tiny moon and the 2025 Webb detection of methane gas.