A meteor is a bright streak of light in the sky (a "shooting star" or a "falling star") produced by the entry of a small meteoroid into the Earth's atmosphere. If you have a dark clear sky you will probably see a few per hour on an average night; during one of the annual meteor showers you may see as many as 100/hour. Very bright meteors are known as fireballs; if you see one please report it.

Meteor History

Meteor showers can be very impressive. Samuel Taylor Coleridge's famous lines from The Rime of the Ancient Mariner:

The upper air burst into life!
And a hundred fire-flags sheen,
To and fro they were hurried about!
And to and fro, and in and out,
The wan stars danced between

And the coming wind did roar more loud,
And the sails did sigh like sedge;
And the rain poured down from one black cloud;
The Moon was at its edge

may have been inspired by the Leonid meteor shower that he witnessed in 1797.

Meteorites are bits of the solar system that have fallen to the Earth. Most come from asteroids, including few are believed to have come specifically from 4 Vesta; a few probably come from comets. A small number of meteorites have been shown to be of Lunar (23 finds) or Martian (22) origin.

One of the Martian meteorites, known as ALH84001 (left), is believed to show evidence of early life on Mars.

Though meteorites may appear to be just boring rocks, they are extremely important in that we can analyze them carefully in our labs. Aside from the few kilos of moon rocks brought back by the Apollo and Luna missions, meteorites are our only material evidence of the universe beyond the Earth.

Meteorite Types
Ironprimarily iron and nickel; similar to type M asteroids
Stony Ironmixtures of iron and stony material like type S asteroids
Carbonaceous Chondritevery similar in composition to the Sun less volatiles; similar to type C asteroids

A "fall" means the meteorite was witnessed by someone as it fell from the sky. A "find" means the meteorite was not witnessed and the meteorite was found after the fact. About 33% of the meteorites are witnessed falls. The following table is from a book by Vagn F. Buchwald. Included are all known meteorites (4660 in all, weighing a total of 494625 kg) in the period 1740-1990 (excluding meteorites found in Antarctica).

Meteorite Statistics
Type Fall % Find % Fall Weight Find Weight
Stony 95.0 79.8 15200 8300
Stony-Iron 1.0 1.6 525 8600
Iron 4.0 18.6 27000 435000

A very large number of meteoroids enter the Earth's atmosphere each day amounting to more than a hundred tons of material. But they are almost all very small, just a few milligrams each. Only the largest ones ever reach the surface to become meteorites. The largest found meteorite (Hoba, in Namibia) weighs 60 tons.





The impact of a comet or asteroid about the size of Hephaistos or SL9 hitting the Earth was probably responsible for the extinction of the dinosaurs 65 million years ago. It left a 180 km crater now buried below the jungle near Chicxulub in the Yucatan Peninsula (right).


Here are educated guesses about the consequences of impacts of various sizes:

Impactor Diameter (meters)Yield (megatons)Interval (years) Consequences
< 50 < 10 < 1 meteors in upper atmosphere most don't reach surface
75 10 - 100 1000 irons make craters like Meteor Crater; stones produce airbursts like Tunguska; land impacts destroy area size of city
160 100 - 1000 5000 irons,stones hit ground; comets produce airbursts; land impacts destroy area size of large urban area (New York, Tokyo)
350 1000 - 10,000 15,000 land impacts destroy area size of small state; ocean impact produces mild tsunamis
700 10,000 - 100,000 63,000 land impacts destroy area size of moderate state (Virginia); ocean impact makes big tsunamis
1700 100,000 - 1,000,000 250,000 land impact raises dust with global implication; destroys area size of large state (California, France)
Data from 'The Impact Hazard', by Morrison, Chapman and Slovic, published in Hazards due to Comets and Asteroids

More recent studies indicate a slightly lower frequency.

More about Meteorites

Open Issues


Here is what President of the United States Bill Clinton had to say about the discovery of evidence for life in a meteorite from Mars:

