What Is the Difference Between a Comet and an Asteroid?

Learn how to tell these two space rocks apart... it’s easier than you think!

Have you ever looked up at the sky and wondered what’s flying around out there? You might have heard of comets and asteroids, but what’s the difference between the two? They both orbit the Sun. They both move through space. And they’re both pretty old. But they’re not the same thing!

Let’s break it down in a way that’s easy to understand.

What is an asteroid?

An asteroid is a rocky space object. Think of it like a giant space rock that didn’t become part of a planet when the solar system formed.

• What it’s made of: Mostly rock and metal

• Where you’ll find them: Mostly in the asteroid belt between Mars and Jupiter

• Do they have tails? No tails—they’re dry and don’t create a visible glow

• Size: Some are as small as a pebble, others are hundreds of miles wide

• Fun fact: The asteroid that caused the dinosaurs to go extinct was about 6 miles wide

Asteroids usually stay put in their orbits and don’t have bright trails or flashy features.

What is a comet?

A comet is made of ice, dust, and rock. People often call them “dirty snowballs.” When a comet gets close to the Sun, it heats up and releases gas and dust, creating a glowing tail.

• What it’s made of: Ice, dust, gas, and some rock

• Where you’ll find them: Mostly in the Kuiper Belt or Oort Cloud—far beyond Neptune

• Do they have tails? Yes—when they get near the Sun, they grow bright tails

• Size: Usually smaller than most asteroids, but can have long glowing trails

• Fun fact: Comet tails can be millions of miles long!

Because comets are made of ice, they’re more active when they get warm—meaning when they fly close to the Sun.

So what’s the difference between a comet and an asteroid?

Here’s a quick way to remember:

Feature	Asteroid	Comet
Made of	Rock and metal	Ice, dust, gas, and rock
Location	Asteroid belt	Kuiper Belt or Oort Cloud
Tail?	No	Yes, when near the Sun
Appearance	Dull and rocky	Bright, glowing with a long tail
Activity near Sun	No big change	Gets hot, releases gas and dust

Are they dangerous?

Most comets and asteroids are harmless. But scientists keep an eye on them just in case. If something very large were heading toward Earth, scientists might try to push it off course. (Yes, just like in the movies—except more math and fewer explosions.)

Fun facts about comets and asteroids

• The word “asteroid” means “star-like” in Greek—even though they’re not stars.

• The most famous comet is Halley’s Comet—it visits Earth every 76 years!

• NASA has landed a spacecraft on an asteroid and collected samples from a comet.

• Some scientists think comets may have brought water to Earth billions of years ago.

• There are millions of asteroids and trillions of comets in our solar system!

Comets and asteroids may look similar from far away, but they’re made of very different stuff. Asteroids are dry, rocky, and quiet. Comets are icy, flashy, and dramatic when they swing by the Sun.

So next time you hear about something zooming through space, see if you can guess—is it a comet or an asteroid?