PlayInfoBox

Home /Education /Types of Objects in the Solar System

Types of Objects in the Solar System

Tap an object type to see how it is defined.

Planet

Orbits the Sun, has enough gravity to pull itself into a round shape, and is massive enough to have cleared its orbital neighborhood of other debris. The solar system has eight of them.

Dwarf planet

Meets most of the same conditions as a planet but hasn't cleared its orbital neighborhood. Pluto was reclassified from planet to dwarf planet in 2006 when this distinction was formally adopted.

Moon (natural satellite)

Orbits a planet or dwarf planet. Earth has one; Jupiter and Saturn each have dozens of confirmed moons.

Asteroid

A small, rocky object too small to be classified as a planet, mostly found in the asteroid belt between Mars and Jupiter.

Comet

A body of ice and dust that grows its characteristic bright tail as its ice vaporizes on approach to the Sun.

Meteoroid

A small fragment of rock or metal drifting through space -- called a "meteor" if it burns up entering Earth's atmosphere, and a "meteorite" if part of it survives to reach the ground.

Why Pluto was reclassified

In 2006 the International Astronomical Union added a new formal requirement to the definition of "planet": having cleared the neighborhood around its orbit of other similarly sized objects. Because Pluto shares its orbital region with numerous other bodies of comparable size, it was reclassified as a dwarf planet -- a clear example of how a scientific category can shift as understanding and definitions evolve.

Want more detail on a specific category?

This guide covers the six broad categories at a glance. For a deeper look at each of the eight planets individually -- size, moons, and other facts -- or a closer comparison of exactly how comets and asteroids differ, separate guides cover those in more depth.

Frequently Asked Questions

How many dwarf planets are there in the solar system?

Besides Pluto, the International Astronomical Union has officially recognized several others, including Eris, Ceres, Makemake, and Haumea.

What's the easiest way to tell a comet from an asteroid?

Composition is the biggest giveaway -- a comet is icy enough to visibly vaporize and grow a tail as it nears the Sun, while an asteroid is mostly rock and shows no such visible change.