What are the dwarf planets in our solar system?

The International Astronomical Union (IAU) officially recognizes five dwarf planets: Pluto, Eris, Haumea, Makemake, and Ceres. Pluto, Eris, Haumea, and Makemake orbit beyond Neptune in the Kuiper Belt and scattered disk; Ceres orbits in the asteroid belt between Mars and Jupiter.

Why is Pluto a dwarf planet and not a planet?

In 2006, the IAU defined a planet as a body that (1) orbits the Sun, (2) has enough mass to be roughly spherical, and (3) has 'cleared the neighborhood' around its orbit. Pluto meets the first two criteria but fails the third — it shares its orbital region with thousands of other Kuiper Belt objects of similar size. So it was reclassified as a dwarf planet.

Which dwarf planet is the largest?

Pluto is the largest dwarf planet by diameter at about 2,377 km, slightly larger than Eris (2,326 km). However, Eris is more massive — about 27% more mass than Pluto — because it is denser. So depending on whether you measure by size or weight, you get a different answer.

Ceres is the only dwarf planet in the inner solar system. It orbits in the asteroid belt between Mars and Jupiter and accounts for about a third of the asteroid belt's total mass. With a diameter of 940 km, it is small enough that gravity barely rounds it. NASA's Dawn spacecraft orbited Ceres from 2015 to 2018 and discovered surprisingly bright salt deposits in its craters.

How many dwarf planets are there?

Five are officially recognized by the IAU: Pluto, Eris, Haumea, Makemake, and Ceres. But astronomers have identified dozens of strong candidates, including Sedna, Quaoar, Orcus, and Gonggong. NASA estimates that more than 100 dwarf planets likely exist in the Kuiper Belt and beyond, with thousands more potentially in the scattered disk and Oort Cloud.

Where are most of the dwarf planets located?

Four of the five recognized dwarf planets — Pluto, Eris, Haumea, and Makemake — orbit beyond Neptune in the Kuiper Belt or scattered disk. They are sometimes grouped as 'plutoids' or 'trans-Neptunian objects.' Ceres is the lone exception, orbiting in the asteroid belt between Mars and Jupiter.

May 2, 2026

Dwarf Planets in Our Solar System: A Complete Guide

Our solar system has five officially recognized dwarf planets: Pluto, Eris, Haumea, Makemake, and Ceres. Four of them orbit beyond Neptune in a frozen, sparsely populated region called the Kuiper Belt. The fifth, Ceres, sits much closer to home, in the asteroid belt between Mars and Jupiter. Together they tell a story about how astronomers redefined the word "planet" in 2006 — and why Pluto, the most famous of them, lost its planethood without losing any of its weirdness.

Distant view of stars and a small icy world — illustrating the outer solar system

Photo: Unsplash

The Five Dwarf Planets at a Glance

Name	Diameter	Region	Discovered
Pluto	2,377 km	Kuiper Belt	1930 (Tombaugh)
Eris	2,326 km	Scattered disk	2005 (Brown et al.)
Haumea	~1,560 km (long axis)	Kuiper Belt	2004 (Brown et al.)
Makemake	~1,430 km	Kuiper Belt	2005 (Brown et al.)
Ceres	940 km	Asteroid belt	1801 (Piazzi)

Note the gap: every dwarf planet on this list is smaller than Earth's Moon. Even the largest, Pluto, is about two-thirds the Moon's diameter. For context, see our guide on comparing planets at scale.

What Is a Dwarf Planet? The IAU Definition

In 2006, the International Astronomical Union met in Prague and voted on a formal definition of "planet." The vote was prompted by the 2005 discovery of Eris, which was initially reported as "the tenth planet" — and which forced astronomers to confront the obvious question: if Eris is a planet, where do we draw the line, since other Kuiper Belt objects keep getting found?

The IAU's answer was a three-part test for planethood. A body must:

1. Orbit the Sun (not another planet — that rules out moons).
2. Have enough mass that gravity has pulled it into a roughly spherical shape (called "hydrostatic equilibrium").
3. Have cleared the neighborhood around its orbit — meaning it is gravitationally dominant in its orbital zone.

A dwarf planet meets criteria 1 and 2 but fails criterion 3. It orbits the Sun and is massive enough to be round, but it shares its orbital region with comparable bodies. Pluto, sharing its zone with thousands of other Kuiper Belt objects, fails the third test. So does Eris, Haumea, Makemake, and Ceres.

Pluto: The Most Famous Dwarf Planet

Discovered in 1930 by Clyde Tombaugh at Lowell Observatory in Arizona, Pluto was treated as the ninth planet for 76 years. It is about 2,377 km in diameter, smaller than Earth's Moon, and orbits the Sun once every 248 Earth years. Its orbit is dramatically tilted (17 degrees from the ecliptic) and so eccentric that for 20 years out of every 248, Pluto is closer to the Sun than Neptune.

Pluto has five known moons. Charon, the largest, is so big relative to Pluto (roughly half its diameter) that the two orbit a shared center of gravity outside Pluto itself, making them effectively a binary system. The other moons — Styx, Nix, Kerberos, and Hydra — are all small and irregular.

In July 2015, NASA's New Horizons spacecraft made the first close flyby of Pluto, returning images of a stunningly varied surface: nitrogen ice plains, water-ice mountains, possible cryovolcanoes, and the now-iconic heart-shaped Tombaugh Regio. The flyby transformed Pluto from a distant point of light into a real, complicated world.

Eris: The One That Started It All

Eris was discovered in 2005 by Mike Brown, Chad Trujillo, and David Rabinowitz at Palomar Observatory. It is slightly smaller than Pluto in diameter (about 2,326 km) but about 27% more massive — its higher density tips the scales. Eris orbits in the scattered disk, an outer extension of the Kuiper Belt, and takes 558 Earth years to circle the Sun.

Eris is the reason the IAU had to act. Its discovery, originally reported as a tenth planet, forced astronomers to confront an awkward future: every new Kuiper Belt giant would arrive as a new "planet," with no end in sight. By creating the dwarf planet category, the IAU drew a line — and Pluto, despite its fame, fell on the wrong side of it. Eris has one known moon, Dysnomia.

Haumea, Makemake, and Ceres

Haumea is the strangest-shaped dwarf planet. Spinning so fast it completes a rotation every 4 hours, Haumea is stretched into an elongated, football-like shape — its long axis is roughly twice the length of its short axis. It has a faint ring (the first dwarf planet known to have one), two small moons (Hi'iaka and Namaka), and a surface dominated by water ice. It orbits in the Kuiper Belt and was discovered in 2004.

Makemake, also discovered in 2005, is roughly 1,430 km across and one of the brightest objects in the Kuiper Belt. Its surface is coated in frozen methane that gives it a reddish color. Makemake has one known moon, MK2, and an orbit that takes about 305 Earth years.

Ceres is the odd one out. Discovered in 1801 by Giuseppe Piazzi, Ceres was originally called a planet, then reclassified as an asteroid for 150 years, and finally upgraded to dwarf planet in 2006. At 940 km across, it is the smallest dwarf planet and the only one in the inner solar system, orbiting in the asteroid belt between Mars and Jupiter. NASA's Dawn spacecraft orbited Ceres from 2015 to 2018 and discovered surprisingly bright salt deposits in its crater Occator — evidence that liquid water once seeped to the surface from a subsurface reservoir.

Are There More? The Probable Dwarf Planets

Five is the official count, but it is almost certainly an undercount. Astronomers have identified several strong candidates that meet the dwarf planet criteria but have not yet been formally classified by the IAU:

Sedna — a deep-red object on an enormous, elongated orbit that takes about 11,400 years to complete. Quaoar — a Kuiper Belt object with a ring system. Orcus — sometimes called the "anti-Pluto" because it orbits in resonance with Neptune in a position opposite Pluto. Gonggong — one of the largest known trans-Neptunian objects, with a moon called Xiangliu.

NASA estimates that more than 100 dwarf planets likely exist in the Kuiper Belt and beyond, with thousands more potentially in the scattered disk and the hypothesized Oort Cloud. As survey telescopes get more sensitive, the list will keep growing. The five we have now are simply the ones bright enough or close enough to confirm.

Explore the Solar System

See how dwarf planets compare to the rest of the system in the interactive Solar System game. Or test your daily geography and astronomy in the GeoProwl daily game.

For more on the worlds beyond our solar system's edge, read our companion piece on Beyond Pluto: The 5 Dwarf Planets, or step back to the 8 main planets in order and the staggering scale of the solar system.