Short answer
In the IAU Solar System classification, a planet orbits the Sun, is nearly round under its own gravity and has cleared its orbital neighborhood. A dwarf planet meets the first two conditions but has not cleared its neighborhood. Pluto is a dwarf planet, not the ninth planet under that definition. 1 2
Both orbit the Sun and are nearly round; orbital-neighborhood criterion separates the formal Solar System classes.
On this page
At a glance
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| Question | Planet | Dwarf planet |
|---|---|---|
| Orbits Sun | Yes | Yes |
| Nearly round | Yes | Yes |
| Cleared orbital neighborhood | Yes | No |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Planet. Under the IAU Solar System definition, a body orbiting the Sun that is nearly round and has cleared its orbital neighborhood. 1
Dwarf planet. A nearly round body orbiting the Sun that has not cleared its orbital neighborhood and is not a satellite. 2
Key differences
“Cleared” does not mean the orbit contains absolutely no debris. It means the body is gravitationally dominant among nearby bodies over time. Size alone is therefore not the decisive rule, even though roundness is part of both definitions. 1 2
The Solar System rule combines two different tests: gravity makes the body nearly round, and its long-term interaction with neighbors determines whether it dominates its orbital zone. Pluto passes the roundness test but not the dynamical one. Earth also shares its orbit with small debris, yet it gravitationally dominates its vicinity in the intended sense. 1 2
How to tell them apart
For a named Solar System body, first establish that it orbits the Sun and is nearly round, then ask whether it dominates the region of its orbit. Pluto shares the Kuiper Belt region with many objects, so it falls into the dwarf-planet category. 1 2
Where they overlap
The two classes share orbit and shape criteria. Dwarf planets are planet-like in some physical respects but are a separate formal class under the IAU scheme. 1 2
Edge cases
The IAU wording was made for bodies orbiting the Sun; classification of exoplanets needs other working definitions. Some researchers debate the usefulness of clearing as a boundary, so the category is a convention as well as a physical description. 1 2
The word “dwarf” can misleadingly suggest a size-only subclass of planet. Under the IAU resolution it names a distinct category. The rule is formally phrased for Sun-orbiting bodies, so applying its exact wording to planets around other stars without specifying a convention invites confusion. 1 2
Why the distinction exists
The classification responds to discoveries of additional round objects beyond Neptune. It groups bodies using both physical shape and dynamical role in an orbit. 1 2
Common misconceptions
A dwarf planet is not simply a small planet: the orbital-neighborhood criterion matters. Also, “cleared” does not mean an empty orbit. 1 2
Examples
Earth is a planet in this scheme; Pluto is a dwarf planet despite being round and orbiting the Sun. 1 2
Sources
Sources checked October 3, 2026.
- NASA Science — What Is a Planet?. The IAU definition of a planet; Pluto.
- NASA Science — Pluto & Dwarf Planets. Dwarf planet overview.