DEFINITION OF METEOR

Rocky objects from space that strike the Earth.

When meteorites pass through Earth’s atmosphere, they get

heated and their surfaces become ionized, causing them to

glow brightly and form a streak moving across the atmosphere

known as a shooting star or fireball.

At certain times of the year, the Earth passes through

parts of our solar system that are rich in meteorites, and the

night skies become filled with shooting stars and fireballs,

sometimes as frequently as several per minute. These times of

high-frequency meteorite encounters are known as meteor

showers and include the Perseid showers that appear around

August 11 and the Leonid showers that appear about November

14 (both occur annually).

There is ample evidence that many small meteorites have

hit the Earth frequently throughout time. Eyewitness

accounts describe many events, and fragments of meteorites

are regularly recovered from places like the Antarctic ice

sheets, where rocky objects on the surface have no place to

come from but space. Although meteorites may appear as

flaming objects moving across the night skies, they are generally

cold icy bodies when they land on Earth, and only their

outermost layers get heated from the deep freeze of space

during their short transit though the atmosphere.

Meteorites consist of several different main types. Stony

meteorites include chondrites, which are very primitive and

ancient meteorites made of silicate minerals, like those common

in the Earth’s crust and mantle, but chondrites contain

small spherical objects known as chondrules. These chondrules

contain frozen droplets of material that is thought to

be remnants of the early solar nebula from which the Earth

and other planets initially condensed. Achondrites are similar

to chondrites in mineralogy, except that they do not contain

the chondritic spheres. Iron meteorites are made of an ironnickel

alloy with textures that suggest they formed from slow

crystallization inside a large asteroid or small planet that has

since been broken into billions of small pieces, probably by

an impact with another object. Stony-irons are meteorites

that contain mixtures of stony and iron components and

probably formed near the core-mantle boundary of the broken

planet or asteroid. Almost all meteorites found on Earth

are stony varieties.

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