# Comets, Asteroids and Meteors: What's the Difference?

> Comets, asteroids, meteoroids, meteors and meteorites are easy to confuse. This guide explains what each one is, what they are made of, where they come from, and why a comet grows a tail.

*Section: Science — By Dr. Nadia Okoro (Science & Health Writer) — Published January 18, 2025 — 5 min read*

Canonical URL: https://dailyjunction.org/science/how-do-comets-and-asteroids-differ
Tags: comets, asteroids, meteors, astronomy, solar system

## Key takeaways

- Asteroids are rocky or metallic bodies, mostly orbiting between Mars and Jupiter.
- Comets are icy bodies from the outer solar system that grow glowing tails when near the Sun.
- A meteoroid is a small fragment of rock or debris travelling through space.
- A meteor is the streak of light, a shooting star, made when a meteoroid burns up in the atmosphere.
- A meteorite is a fragment that survives the fall and lands on the ground.

Comet, asteroid, meteor, meteoroid, meteorite. These words get used almost interchangeably in everyday speech, yet each describes something distinct. Some are icy, some are rocky; some live in deep space, some streak through our sky; some burn up entirely, while others crash to the ground. Sorting them out is one of the most satisfying small lessons in astronomy, and it reveals a lot about the leftovers from which our solar system was built.

## What these objects are

**Comets, asteroids and meteoroids are all small bodies left over from the formation of the solar system; the differences lie in what they are made of, where they come from, and what we call them at different stages.** Meteors and meteorites are not separate kinds of object at all, but names for what happens when a small body meets Earth.

Together these objects are sometimes called the "small bodies" of the solar system, in contrast to the planets and moons. They are ancient, dating back over four and a half billion years, and studying them is like reading the construction notes of the planets themselves.

## Asteroids: the rocky leftovers

An **asteroid** is a rocky or metallic body that orbits the Sun, far smaller than a planet. Most asteroids are found in the **asteroid belt**, a broad region between the orbits of Mars and Jupiter, though some follow paths that bring them closer to Earth.

A few key points about asteroids:

- They are made mainly of **rock and metal**, with little or no ice.
- They range enormously in size, from tiny boulders to bodies hundreds of kilometres across.
- They are thought to be material that never managed to come together into a planet, partly because of Jupiter's powerful gravity stirring the region.

Despite films suggesting otherwise, the asteroid belt is mostly empty space; the asteroids within it are typically millions of kilometres apart.

## Comets: the icy visitors

A **comet** is a body made largely of **ice, dust and rock**, often described as a "dirty snowball". Comets originate in the cold, distant reaches of the solar system, far beyond the planets, and travel on long, stretched orbits that occasionally bring them close to the Sun.

What makes comets so distinctive is what happens on that approach. As a comet nears the Sun and warms up:

1. Its surface ice turns straight from solid to gas, a process called sublimation.
2. This releases gas and dust, forming a glowing, fuzzy cloud around the comet's solid core, known as the **coma**.
3. Radiation and the stream of particles flowing from the Sun, the solar wind, push this material outward into one or more **tails**.

A comet's tail always points roughly away from the Sun, regardless of which way the comet is travelling, because it is blown outward by the Sun rather than trailing behind like smoke. Famous comets such as Halley's return on predictable schedules, their orbits worked out through exactly the kind of careful observation and testing described in our guide to [the scientific method](/science/what-is-the-scientific-method).

## Comet versus asteroid at a glance

The simplest way to hold the distinction in mind is a quick comparison.

| Feature | Asteroid | Comet |
|---------|----------|-------|
| Made of | Rock and metal | Ice, dust and rock |
| Usual home | Asteroid belt, inner solar system | Outer solar system |
| Tail? | No | Yes, when near the Sun |
| Orbit shape | Usually more circular | Often long and stretched |

The line between the two is not always perfectly sharp; some objects share features of both. But as a rule of thumb, rocky and inner means asteroid, icy and far means comet.

## Meteoroids, meteors and meteorites

This trio causes the most confusion, yet the distinction is simply about location and stage.

- A **meteoroid** is a small fragment of rock or debris travelling through space, often a chip off an asteroid or the dusty trail left by a comet. Think of it as a small object still out in space.
- A **meteor** is the streak of light produced when a meteoroid enters Earth's atmosphere and burns up due to friction and heat. This is what people call a **shooting star**, even though no star is involved.
- A **meteorite** is a fragment that survives its fiery passage through the atmosphere and lands on the ground.

So the same piece of material can change name three times: a meteoroid in space, a meteor as it blazes through the sky, and a meteorite once it has landed. The order of these terms never changes, much like the fixed sequence of colours explained in our guide to [how rainbows form](/science/how-do-rainbows-form).

## Meteor showers and where they come from

Several times a year, Earth passes through the trail of dusty debris left behind by a comet. When it does, many meteoroids enter the atmosphere at once, producing a **meteor shower** with dozens of shooting stars an hour. Well-known examples such as the Perseids in August and the Geminids in December recur on the same dates each year, because Earth crosses the same debris streams as it orbits the Sun, the same orbital regularity that underlies [what causes the seasons](/science/what-causes-the-seasons).

These showers are completely harmless and are a wonderful, free spectacle, best seen from a dark spot away from city lights on a clear night.

## Do they pose a danger?

Most asteroids and comets pose no risk to Earth whatsoever. A small number follow paths that bring them relatively close, and these "near-Earth objects" are tracked carefully by agencies such as NASA and ESA. Large impacts, of the kind linked to the extinction of the dinosaurs, are extremely rare on human timescales. Space agencies even run missions to study how the path of a threatening object might one day be nudged aside, turning a once-mythical danger into a manageable engineering problem.

## The bottom line

Asteroids are rocky or metallic bodies, mostly orbiting between Mars and Jupiter. Comets are icy bodies from the outer solar system that grow a glowing coma and tail when they near the Sun. A meteoroid is a small fragment in space; a meteor is the streak of light it makes burning up in our atmosphere; and a meteorite is the piece that survives to reach the ground. Far from being interchangeable, each word marks a real distinction, and together they tell the story of the ancient rubble from which the planets, and we, ultimately came.

## Frequently asked questions

### What is the difference between a comet and an asteroid?

An asteroid is a rocky or metallic body, mostly found orbiting between Mars and Jupiter. A comet is made largely of ice and dust and comes from the cold outer solar system. When a comet nears the Sun, its ice turns to gas and it grows a glowing coma and tail, which asteroids do not.

### What is the difference between a meteoroid, a meteor and a meteorite?

A meteoroid is a small piece of rock or debris in space. If it enters Earth's atmosphere and burns up, the streak of light it creates is a meteor, often called a shooting star. If a fragment survives and lands on the ground, that piece is a meteorite.

### Why do comets have tails?

As a comet approaches the Sun, its surface ice warms and turns straight to gas, releasing dust and forming a fuzzy cloud called a coma. Solar radiation and the solar wind push this material outwards, creating one or more tails that always point roughly away from the Sun.

### Are asteroids and comets dangerous to Earth?

Most pose no threat, but some pass close to Earth and are tracked carefully by space agencies. Large impacts are very rare on human timescales. Agencies such as NASA and ESA run programmes to monitor near-Earth objects and study how an impact might one day be prevented.

## Sources

- [NASA: Asteroids, Comets and Meteors](https://science.nasa.gov/solar-system/)
- [European Space Agency (ESA): Comets and asteroids](https://www.esa.int/Science_Exploration/Space_Science)
- [Royal Museums Greenwich: Meteors and meteorites](https://www.rmg.co.uk/)

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