Comet vs. Asteroid: What's the Difference?
Comets and asteroids are both leftovers from the early Solar System, but they're made of different stuff and come from different places. A comet is mostly ice and dust that vaporizes into a glowing tail when it nears the Sun; an asteroid is mostly rock and metal that stays solid and tail-less.
See the difference, explained visually.
Watch a 2-minute animated lesson comparing comet and asteroid.
At a glance
| Comet | Asteroid | |
|---|---|---|
| Made of | Ice, dust, frozen gases | Rock and metal |
| Tail | Yes — glows near the Sun | No tail |
| Origin | Outer Solar System (cold, distant) | Mostly the asteroid belt |
| Orbit | Often long and stretched | Usually more circular, inner system |
| Looks like | Fuzzy glow with a tail | A faint point of light |
Which should you use?
Comet
You're looking at a comet when an object grows a bright coma and tail as it approaches the Sun — the heat turns its ice straight to gas, releasing dust that catches sunlight.
Asteroid
You're looking at an asteroid when the object stays a compact, rocky body with no tail — most orbit the Sun in the asteroid belt between Mars and Jupiter.
Frequently asked questions
- What's the difference between a meteor and these?
- A meteor is the streak of light when a small fragment (often from a comet or asteroid) burns up in Earth's atmosphere. Comets and asteroids are the larger bodies out in space.
- Can an asteroid become a comet?
- Rarely the line blurs — some 'active asteroids' show faint comet-like activity. But generally their different compositions keep them as distinct categories.
- Which one is linked to the dinosaurs' extinction?
- The leading evidence points to a large asteroid impact about 66 million years ago, though a comet has also been proposed. Either way, it was a massive impacting body.