Dwarf Planets: The Complete Guide to the Solar System’s In-Between Worlds

By Hamza — astrophotographer since 2008, imaging from a remote 12.5″ Ritchey-Chrétien at Deepsky Chile (@stellar.nomads)

Quick answer: A dwarf planet is a round body that orbits the Sun and has not cleared its orbital neighborhood of other objects, and is not a moon. The five bodies the IAU officially recognizes are Ceres, Pluto, Haumea, Makemake, and Eris — though astronomers suspect 100+ more await confirmation.

Dwarf planets are the Solar System’s in-between worlds: too big and too round to be mere asteroids, yet not dominant enough in their orbits to count as full planets. They include the largest object in the asteroid belt (Ceres), the famous demoted ninth planet (Pluto), and three frozen wanderers far beyond Neptune (Haumea, Makemake, and Eris). This page is the dwarf-planets hub within our larger Solar System guide, and it aims to be the single most useful resource on the topic anywhere on the web.

What sets this guide apart is the angle no science encyclopedia or general astronomy site offers: how to actually see and image these worlds. Alongside plain-English explanations of the science — what “clearing the neighborhood” really means, how many dwarf planets exist, and how each one was found — you’ll get the observing details that matter at the eyepiece and the camera: the apparent magnitude of each object, the minimum aperture you need, the best time to catch it near opposition, and how to confirm a faint point of light by tracking its motion across two nights. Some, like Ceres, sit within reach of ordinary binoculars; others, like Eris, demand a 25-inch (or larger) telescope and a dark sky. Wherever it helps, I’ll share first-hand notes from chasing these targets myself.

Table of contents

1. What is a dwarf planet?
2. Dwarf planet vs planet vs asteroid
3. How many dwarf planets are there?
4. The 5 official dwarf planets
5. How dwarf planets compare in size
6. Is Pluto a dwarf planet?
7. Dwarf planet candidates
8. Dwarf planets in order from the Sun
9. How to observe and photograph dwarf planets
10. Frequently asked questions

What is a dwarf planet?

A dwarf planet is a round object that orbits the Sun but has not cleared its orbital neighborhood of other bodies, and it is not a moon. That single sentence captures the whole idea, but the official definition is worth unpacking because it is exactly where dwarf planets split off from the eight major planets.

The rules come from the International Astronomical Union (IAU), which created the category in 2006. Under that resolution, a body must pass three tests to be a full-fledged planet:

1. It orbits the Sun — not another planet (that would make it a moon).
2. It is massive enough to be round. Its own gravity pulls it into a near-spherical shape, a state astronomers call hydrostatic equilibrium.
3. It has “cleared its neighborhood.” Over billions of years it has become gravitationally dominant, sweeping up, flinging away, or capturing the smaller debris that shares its orbit.

A dwarf planet checks boxes 1 and 2 but fails box 3. It circles the Sun and it is round, yet it still shares its lane with a crowd of comparably sized icy or rocky bodies it was never massive enough to push aside. The IAU added one more condition that quietly does a lot of work: a dwarf planet must not be a satellite. That is why our own Moon does not count — it is round, but it orbits Earth rather than the Sun directly, which makes it a satellite, not a dwarf planet.

What does “cleared the neighborhood” actually mean? Think of a planet as a snowplow on a highway. A full planet has plowed its lane clean, so it cruises along essentially alone except for its own moons. A dwarf planet is more like a car stuck in stop-and-go traffic — it stays in its lane, but it is hemmed in by thousands of other vehicles it can never clear. Pluto, for example, is just one of countless icy worlds in the Kuiper Belt; Ceres is one body among many in the asteroid belt. Neither dominates its zone, so neither makes the planet cut.

It is also worth knowing the scale: every dwarf planet is smaller than Earth’s Moon — even the largest, Pluto and Eris, are only about two-thirds the Moon’s diameter — which is one reason the count and the boundaries still spark debate. We dig into the full planet-versus-dwarf-planet contrast in the next section, and the famous test case — Pluto, reclassified under exactly these rules — gets its own deep dive on the dedicated Pluto dwarf planet guide. For how all of this fits the bigger picture, the planets of the solar system page covers the eight worlds that did clear their orbits.

Dwarf planet vs planet vs asteroid

A dwarf planet sits in the middle of three categories the International Astronomical Union uses to sort objects orbiting the Sun. The fastest way to tell them apart is to ask three yes-or-no questions: Is it round? Does it orbit the Sun? Has it cleared its orbital neighborhood?

The single line that separates a planet from a dwarf planet is the third one: a planet has swept its orbital path clean, pulling in or flinging away nearly everything else of comparable size, while a dwarf planet shares its lane with countless similar objects. Pluto, for example, is just one of thousands of icy bodies in the Kuiper Belt, so it fails that test even though it is clearly round.

The line between a dwarf planet and an asteroid is different: it comes down to shape. Asteroids and other small bodies are not massive enough for their own gravity to crush them into a sphere, so they stay irregular, like cosmic potatoes. Ceres is the classic borderline case — it is the largest object in the asteroid belt, but because it is big enough (about 940 km / 584 mi across) to pull itself round, the IAU promoted it to dwarf planet in 2006. It still lives among the asteroids, which is why people often call it both: Ceres is physically located in the asteroid belt, but its category is “dwarf planet,” not “asteroid.” In practical terms, every planet is far larger than every dwarf planet, and every dwarf planet is round while nearly every asteroid is not. Note that none of these three categories includes moons: a body has to orbit the Sun directly, not another planet, to qualify at all. For how each of these worlds fits into the bigger picture, see the solar system overview.

How many dwarf planets are there?

The short answer: five. The International Astronomical Union (IAU) officially recognizes exactly five dwarf planets — Ceres, Pluto, Haumea, Makemake, and Eris. That number has not changed since 2008, when Makemake and Haumea were added to the list (Ceres, Pluto, and Eris came first, in 2006).

But the honest answer is “five officially, with many more waiting in line.” The real count is genuinely fuzzy, and here is why.

Why the number is so hard to pin down

The sticking point is the second IAU rule: to be a dwarf planet, an object must be massive enough that its own gravity pulls it into a round shape (a state called hydrostatic equilibrium). Confirming roundness sounds simple, but most candidates orbit far out in the Kuiper Belt and the trans-Neptunian region, tens to hundreds of times farther from the Sun than Earth. From that distance they appear as little more than dim points of light, even through the world’s largest telescopes. We often cannot measure their exact size, shape, or mass well enough to say for certain.

So the IAU stays conservative and only confirms an object once the evidence is solid. Astronomers, meanwhile, keep a longer working list of bodies they are confident will qualify — Mike Brown’s catalog alone flags dozens of “highly likely” and hundreds of “possible” dwarf planets across its likelihood tiers. New discoveries — like the distant candidate 2017 OF201, announced in May 2025 — keep stretching that list. Every wide-field survey of the outer solar system turns up more icy worlds, which is why “5” is the rule-book answer but almost certainly not the final one.

For the full rundown, see the comparison table of all five official dwarf planets below, then explore the candidate dwarf planets still awaiting recognition.

The 5 official dwarf planets

The International Astronomical Union (IAU) recognizes five dwarf planets. Listed in order of their average distance from the Sun, they are Ceres, Pluto, Haumea, Makemake, and Eris. Only Ceres orbits inside the asteroid belt; the other four are frozen worlds far beyond Neptune in the Kuiper Belt and scattered disk. Every one of them is smaller than Earth’s Moon (about 3,475 km / 2,159 mi across), which tells you just how compact these little worlds really are.

Ceres is the odd one out. It sits in the asteroid belt between Mars and Jupiter, making it the only dwarf planet you can reach without crossing Neptune’s orbit. At about 940 km (584 mi) wide, it holds roughly a third of the entire asteroid belt’s mass. NASA’s Dawn spacecraft orbited Ceres from 2015 to 2018 and found bright salt deposits in Occator Crater, along with strong evidence of briny water and a possible muddy subsurface ocean. Ceres is also the easiest dwarf planet to observe, brightening to roughly magnitude 7 at a favorable opposition, so it shows up in ordinary binoculars.

Pluto is the most famous of the five and the largest by diameter, at about 2,377 km (1,477 mi). When NASA’s New Horizons probe flew past in July 2015, it revealed a stunning, geologically active world with a vast heart-shaped plain of frozen nitrogen ice. Pluto also commands a system of five moons, dominated by Charon, which is so large (about half Pluto’s diameter, roughly 1,212 km / 753 mi) that the two bodies orbit a point in empty space between them. Pluto carries far too much story for this hub page, so we cover its reclassification debate, the New Horizons flyby, and its observing details in depth on the dedicated Pluto dwarf planet guide.

Haumea is the strangest body on this list. It spins so fast, completing one rotation in just 3.9 hours, that its own rotation has stretched it into an egg shape: its longest axis runs roughly 2,100 km (about 1,300 mi), nearly twice the length of its shortest (polar) axis, even though its volume-equivalent mean diameter is only about 1,560 km (970 mi). That rapid spin probably came from an ancient collision, which also produced its two moons, Hiʻiaka and Namaka, and a family of icy fragments scattered nearby. In 2017, astronomers watching Haumea pass in front of a distant star discovered a thin ring around it, about 70 km (40 mi) wide. This was the first ring ever found around a trans-Neptunian object, and the ring particles loop around the planet once for every three times Haumea spins.

Makemake is the second-brightest known object in the Kuiper Belt and trans-Neptunian region after Pluto. About 1,430 km (888 mi) across, it has a reddish surface so reflective and cold that frozen methane and ethane likely coat it like a crust. For years Makemake appeared to be solitary, but it turned out to have a small, dark moon nicknamed MK 2 — roughly 175 km (110 mi) wide — first imaged by the Hubble Space Telescope in 2015 and announced in 2016. The moon’s faintness against its bright parent is exactly why it stayed hidden for so long.

Eris is the heavyweight that changed everything. Although Pluto edges it out in diameter, Eris (about 2,326 km / 1,445 mi) is roughly 27% more massive, making it the most massive dwarf planet of all. Its discovery in 2005 forced astronomers to ask a hard question: if Pluto counts as a planet, why not this slightly heavier twin sitting even farther out in the scattered disk? That debate led directly to the IAU’s 2006 vote and the modern definition of a dwarf planet. Eris has one known moon, Dysnomia, and orbits so far away (around 68 AU on average) that it remains a faint point of light even in large telescopes.

How dwarf planets compare in size

Numbers in a table are one thing; seeing the scale is another. Every dwarf planet is smaller than Earth’s Moon, and most science pages never show you that side by side. Here is how the five official dwarf planets stack up against the Moon and Earth, drawn to scale by diameter.

A few things jump out once you see it laid out. Earth dwarfs the whole group — you could line up more than five Plutos across one Earth. The Moon, which we never think of as small, is bigger than every dwarf planet by a clear margin. And the five dwarf planets themselves split into two tiers: Pluto and Eris are near twins at roughly 2,300–2,400 km, while Ceres is so much smaller (just 940 km) that it would fit inside Pluto with room to spare. That huge spread in size is part of why the category feels so loose, and why the boundary with both planets and asteroids keeps generating debate. Mass tells a slightly different story than diameter, too: Eris is narrower than Pluto but about 27% heavier, because it is denser and packs more rock beneath its ice.

Is Pluto a dwarf planet?

Yes, Pluto is a dwarf planet. The IAU reclassified it from the ninth planet to a dwarf planet in 2006, and it has held that status ever since. It passes the first two planet tests easily — it orbits the Sun and it is round — but it fails the third. Pluto orbits inside the crowded Kuiper Belt, sharing its lane with countless icy bodies and even crossing Neptune’s path, so it has never cleared its neighborhood. That single missed criterion is why it is a dwarf planet rather than a planet.

The trigger was the 2005 discovery of Eris, a world about the same size as Pluto and, as we now know, slightly more massive. If Pluto counted as a planet, Eris had to as well — and many more Pluto-sized bodies were likely waiting in the outer Solar System. Rather than keep adding planets, the IAU wrote a formal definition of “planet” for the first time, and Pluto landed in the new dwarf-planet category. The full story — the five moons, the 2015 New Horizons flyby, the famous nitrogen “heart,” the lingering “geophysical definition” debate, and whether Pluto could ever be a planet again — lives on our in-depth Pluto dwarf planet guide. You can also see where Pluto fits among the icy worlds of the Kuiper Belt and trans-Neptunian objects.

Dwarf planet candidates

Beyond the five worlds the IAU officially recognizes, astronomers have found dozens of bodies in the outer solar system that almost certainly qualify as dwarf planets. They are round (or nearly so) and orbit the Sun far past Neptune, but the IAU has not formally added them to the list. The reason is almost always the same: they are so distant and so faint that confirming they are massive enough to have pulled themselves into a round shape (hydrostatic equilibrium) is extremely hard. Until that roundness is nailed down, they stay “candidates.”

The strongest candidates live in the Kuiper Belt and scattered disk, the icy reservoir of trans-Neptunian objects beyond Neptune’s orbit.

Each of these is large enough that most astronomers treat it as a dwarf planet in practice. Mike Brown, who co-discovered several of them, keeps a running tally that lists dozens of “highly likely” and hundreds of “possible” dwarf planets across the outer solar system. The catalog keeps growing, too: in May 2025, astronomers announced 2017 OF201, a candidate (~700 km across) on an extreme ~25,000-year orbit with a semi-major axis near 840 AU that swings out to roughly 1,600 AU at its farthest, hinting at many more frozen worlds still waiting in the dark.

There is fresh science here as well. In 2024, a long campaign of stellar occultations (datasets gathered from 2011 through 2024) refined Quaoar’s dimensions to roughly 1,167 × 1,111 × 1,020 km and supported a striking idea: Quaoar’s slightly squashed, elongated figure appears to be a “frozen-in” shape. The thinking is that Quaoar was once spinning faster and bulged out under that spin, then its rotation slowed — likely from tidal interaction with its moon Weywot — and the rigid, icy body locked in the old shape instead of relaxing into a perfect sphere. That makes its compliance with hydrostatic equilibrium genuinely ambiguous, which is part of why the IAU has not rushed to promote it.

Spectroscopy is moving fast, too. The James Webb Space Telescope (JWST) has begun taking detailed infrared spectra of trans-Neptunian objects, sorting them into surface-composition families and detecting ices like carbon dioxide, water, and complex carbon-bearing compounds on the faint, far-off candidates that ground telescopes can barely register. Those measurements are exactly the kind of evidence that will eventually push some of today’s candidates onto the official list — and they make the outer Solar System feel less like a blank map every year.

Dwarf planets in order from the Sun

The five IAU-recognized dwarf planets are spread across two very different regions. Ceres orbits close in, within the asteroid belt between Mars and Jupiter. The other four are far out in the cold trans-Neptunian region, beyond the planet Neptune. Distances out there are vast: one astronomical unit (AU) equals the Earth-Sun distance of about 150 million km (93 million mi), so Eris at roughly 68 AU sits more than 10 billion km (6.3 billion mi) from the Sun.

Here are the five official dwarf planets, ordered by their average distance from the Sun:

A few notes on the ordering. These are average distances, and because dwarf-planet orbits are highly elliptical, the real positions overlap and shift over time. Pluto’s orbit, for example, sometimes brings it closer to the Sun than Neptune. Eris swings even farther on its long path, reaching nearly 98 AU at its most distant point.

The likely dwarf planet Sedna sits in a class of its own, far beyond Eris. Its average distance is around 500 AU, and its extreme orbit carries it out past 900 AU at aphelion, taking roughly 11,000 years to circle the Sun once. Objects like Sedna and the 2017 OF201 candidate hint at how much of the outer Solar System we have yet to map.

How to observe and photograph dwarf planets

Here is the honest truth most science pages skip: with the exception of Ceres, dwarf planets are hard targets. None of them shows a disk in an amateur telescope. They appear as faint, star-like points, and the only way you confirm you’ve actually caught one is by photographing the same field on two or three nights and watching your point of light shift against the fixed background stars. That slow crawl is the proof. You are not resolving a world; you are detecting motion.

Observing difficulty, easiest to hardest:

Ceres is genuinely fun and accessible: around magnitude 7 at opposition, it is brighter than Neptune and easily reaches binoculars or a small scope even under suburban light pollution. Sweep the right star field, note the one “star” that isn’t on your chart, and come back the next clear night. Pluto is the classic rite of passage. At magnitude 14-plus it demands a 10-inch or larger scope, a transparent sky, and patience to match it against the background over several nights. Haumea, Makemake, and Eris belong to deep-imaging specialists with large apertures and stacked exposures.

The candidates raise the bar even higher. Quaoar and Eris both sit near magnitude 18.7–18.9, faint enough that you really want a 25–30-inch (or larger) instrument and clean stacking to pull them out of the noise. Orcus is similar at around magnitude 19. Gonggong (~21.5) and Sedna (~20.5–21) are effectively beyond visual reach for amateurs — they are observatory-class targets, recorded only in long exposures by large telescopes. If you set out to image a candidate, treat it exactly like the faint official ones: plan around opposition, shoot multiple nights, and let the object’s motion confirm the catch.

This is where I can speak from experience. I’ve imaged from a remote 12.5-inch Alluna Ritchey-Chrétien with an SBIG STL-11000 at Deepsky Chile, and even with that aperture under Bortle 1 skies, Ceres and Pluto never showed as discs — at the rig’s plate scale they landed as a single faint 1–2 pixel dot, indistinguishable from the field stars on any one frame. The way I confirmed each one was the old-fashioned way: shoot the same field on two separate nights, register the frames on the background stars, then blink the two stacks back and forth. The one “star” that has hopped a few pixels between sessions is your target. That little jump is the entire payoff — not a picture of a world, but proof you tracked a body billions of kilometers away across the sky. It is a quiet, slow thrill, and it never gets old. (More about the rig and how I work on the about page.)

A few StellarNomads tools make the planning much easier:

• Use the FOV simulator to frame Ceres near opposition for your exact scope and camera, so you know which star field to shoot and can spot the interloper fast when you blink your two nights together.
• Run the sub-exposure calculator to plan exposure length for the magnitude-17-plus targets like Makemake and Haumea, swamping read noise without blowing out nearby stars.
• The all-in-one astrophotography calculator dials in your image scale and sampling for the faint, point-source TNOs, so a candidate like Quaoar lands cleanly across your subs.

Plan around opposition, when each object sits highest and brightest, check a current ephemeris for its precise position, and let movement be your confirmation.

Frequently asked questions

What is a dwarf planet?
A dwarf planet is a round body that orbits the Sun but has not cleared its orbital neighborhood of other debris, and is not a moon of another planet. It meets two of the three criteria for full planethood but fails the third, which is why it sits in its own category.

How many dwarf planets are there?
There are 5 officially recognized by the International Astronomical Union (IAU): Ceres, Pluto, Haumea, Makemake, and Eris. Many astronomers commonly accept about 9 (adding Quaoar, Sedna, Gonggong, and Orcus), and NASA notes there may be 100 or more dwarf planets in the solar system, with some estimates running into the hundreds as we survey the outer regions.

Is Pluto a dwarf planet?
Yes. Pluto was reclassified from the ninth planet to a dwarf planet in 2006 because it shares its region of the Kuiper Belt with countless other icy bodies and has not cleared its orbit. We cover the full reclassification story on the dedicated Pluto guide.

Will Pluto ever be a planet again?
Probably not under the current rules — Pluto still shares its lane in the Kuiper Belt, so it still fails the “cleared its neighborhood” test. The official answer could only change if the IAU adopted a different definition, and some scientists do push for a “geophysical” definition (round equals planet) that would restore it. For now, though, Pluto remains a dwarf planet. The full case for and against lives on our Pluto guide.

Is the Moon a dwarf planet?
No. Our Moon is round and large, but it orbits Earth rather than the Sun directly, which makes it a natural satellite, not a dwarf planet. To qualify as any kind of planet — full or dwarf — a body has to orbit the Sun on its own, not circle another world.

What are the 5 dwarf planets?
In order from the Sun, they are Ceres (in the asteroid belt), then Pluto, Haumea, Makemake, and Eris (all in the Kuiper Belt and trans-Neptunian region).

What is the largest dwarf planet?
It depends on how you measure. Pluto is the largest by diameter at about 2,377 km (1,477 mi), while Eris is the most massive, packing roughly 27% more mass into a slightly smaller ball about 2,326 km (1,445 mi) across. Eris’s higher density is why it tips the scales despite being narrower.

What is the smallest dwarf planet?
Among the 5 official dwarf planets, Ceres is the smallest at roughly 940 km (584 mi) across. It is also the only one in the asteroid belt rather than the outer solar system.

Is Ceres a dwarf planet, an asteroid, or both?
Its category is “dwarf planet.” Ceres was the first object ever called an asteroid (in 1801), and it still physically lives in the asteroid belt, which is why people often describe it as both. But in 2006 the IAU reclassified it as a dwarf planet because it is large enough to be rounded by its own gravity — something true asteroids are not. So it is a dwarf planet that happens to orbit among the asteroids, and the only one in the inner solar system.

What is the difference between a dwarf planet and a planet?
Both orbit the Sun and are massive enough to be round. The difference is that a true planet has cleared its orbital path of other bodies, while a dwarf planet has not. Every dwarf planet is also smaller than Earth’s Moon.

Can you see dwarf planets with a telescope?
Some, yes. Ceres reaches magnitude 7 to 9 near opposition and is visible in binoculars or a small telescope, while Pluto (mag ~14.4) needs a 10-12 inch scope. Haumea, Makemake, and Eris (mag 17 to 19) require 16-30 inch apertures, and you confirm them by their slow drift against the stars over a night or two. Use our FOV simulator and sub-exposure calculator to plan these faint targets.

Will there be more dwarf planets?
Almost certainly. Candidates like Sedna, Quaoar, Gonggong, and Orcus already await confirmation, and the May 2025 discovery of 2017 OF201 on a roughly 840-AU orbit shows how many remain hidden. Most are simply too far and too dim for us to confirm their roundness yet, so the official count will keep growing as telescopes — and instruments like JWST — improve.

About the author: Hamza has been an astrophotographer since 2008, capturing the deep sky from a remote rig at Deepsky Chile — a 12.5-inch Alluna Ritchey-Chrétien on a Paramount MX+ with an SBIG STL-11000 CCD, under the Bortle 1 skies of the Chilean Andes. He has chased faint solar-system targets like Ceres and Pluto across multiple nights to confirm their motion firsthand. Follow his work on Instagram @stellar.nomads.

Ready to hunt a dwarf planet yourself? Start with the FOV simulator to frame Ceres near opposition, plan your faint-target exposures with the sub-exposure calculator, and dial in sampling for the distant TNOs using the all-in-one astrophotography calculator. Then work your way back up to the Solar System hub to explore the planets, asteroids, and the Kuiper Belt.