News about space rocks mixes these words constantly. They mean different things, and once you know the difference, headlines about Apophis make a lot more sense.
A rocky or metallic body that orbits the Sun, smaller than a planet. Most live in the main asteroid belt between Mars and Jupiter. Sizes range from a few meters to hundreds of kilometers. Apophis is an asteroid, about 340 meters wide.
A body made mostly of ice, dust and rock, often called a "dirty snowball." When a comet gets close to the Sun, its ice vaporizes and creates a glowing cloud (coma) and a tail that always points away from the Sun. Comets usually come from the cold outer solar system. Apophis has no tail, so it is not a comet.
A small piece of rock or metal in space, from the size of a grain of sand up to about a meter. Meteoroids are often fragments broken off from asteroids or comets.
The streak of light you see when a meteoroid enters Earth's atmosphere and burns up from friction. This is what people call a "shooting star." A meteor is the light, not the rock.
A meteor that is exceptionally bright, brighter than the planet Venus, is called a fireball. If it explodes in the atmosphere, it is sometimes called a bolide.
A piece that survives the trip through the atmosphere and lands on Earth's surface. Meteorites are valuable to scientists because they are samples of the early solar system.
Meteoroids hit the upper atmosphere at speeds from about 11 to 72 kilometers per second. The air in front of them is compressed and heated so strongly that the surface glows and vaporizes, usually at heights of roughly 80 to 120 kilometers. That glowing trail is the meteor. Most meteoroids are tiny, so they burn up completely. Only the larger, tougher ones, mostly pieces of asteroids, survive as meteorites.
The difference is not only about vocabulary. Asteroids and comets behave differently, and that affects how we study and track them. Comets can be active and unpredictable: as they warm up, they release gas and dust, and the pressure of that outflow can change their orbit. Asteroids are usually calmer, so their paths can be predicted far ahead. That is one reason astronomers can say with confidence that Apophis will not hit Earth in 2029, while comets coming from the far outer solar system are harder to forecast and are typically found with much less warning.
Meteors, yes: on a dark night you can see a few every hour, and many more during a meteor shower. Bright comets appear only once in a few years, and you can usually spot them with binoculars. Most asteroids are too faint for the naked eye. Apophis is a rare exception: during its 2029 flyby it will briefly be bright enough to see without equipment from parts of Europe, Africa and Asia. Read more in our guide on how to watch the flyby.
Is a shooting star a star? No. It is a small piece of space rock burning up in our atmosphere.
Are meteorites dangerous? Rarely. Most are small and cool by the time they reach the ground. Pieces of the 2013 Chelyabinsk event are among the largest recovered in recent years.
Can an asteroid become a comet? Some objects blur the line. Scientists have found "active asteroids" that show comet-like dust tails, so the categories are useful but not perfectly sharp.
| Term | Where is it? | What is it? |
|---|---|---|
| Asteroid | Orbiting the Sun | Rocky/metal body, meters to hundreds of km |
| Comet | Orbiting the Sun | Ice and dust, grows a tail near the Sun |
| Meteoroid | In space | Small rock, grain to about a meter |
| Meteor | In the atmosphere | The streak of light |
| Meteorite | On the ground | The surviving piece |
Now you can read the news with confidence. Next, learn what makes Apophis special or how it compares to the dinosaur asteroid.
Facts in this article are drawn from public scientific sources. For primary information, see: