What is a Meteorite & where do they come from?

Firstly, let's get some terminology out of the way. There is also a full 'Glossary of Meteorite Terms & Definitions' to help.

• Meteoroid - is a small piece of dust, rock, ice or metal moving through space. They are at least the size of a speck of dust but smaller than an asteroid.

• Meteor - is a meteoroid that has entered the Earths atmosphere and burns brightly leaving a flaming tail and sometimes smoke. They are more commonly called 'Shooting Stars' or 'Falling Stars'. Most meteors will burn up completely in the atmosphere.

• Meteorite - is a meteoroid that has survived entry through the atmosphere and reached the Earths surface.

There are some more interesting facts about Meteoroids and their journey through the Earths atmosphere. These can be seen here.

What is a Meteorite? - Just like Earth rocks, meteorites are all different. There are many various types which can be sorted into three main groups. These are:

• Stony - meteorites made up of stone type material and minerals. They will usually have a small amount of Iron/Nickel visible. Stony meteorites can be further broken down into 2 main groups. These are:

• Chondrites - (kon-drites) meteorites which contain chondrules. Chondrules are minerals which formed small spheres while floating around in space. Click Here for excellent examples of chondrules. Chondrites also make up the vast majority of recovered meteorites.

• Achondrites - (a-kon-drites) meteorites which do not contain chondrules. Many of these specimens originate from larger 'parent bodies' such as the Moon, Mars or an asteroid. Some Achondrites may also be melted or transformed Chondrites. For a list of some meteorites and their origins, please click here.

• Stony/Iron - meteorites composed of iron-nickel metal (metallic iron) and stone-type materials in roughly equal proportions.

• Iron - meteorites composed mainly of iron and nickel.

Where Do Meteorites Come From? - Many meteorites are thought to be remnant 'building blocks' of our Solar System which were not used up to make up any of the planets, moons, asteroids, etc. These pieces drift through our Solar System until they hit or are caught in the gravity of a larger body such as Earth.  Also, as mentioned above under Achondrites, there is a theory that some meteorites also originate from existing 'Parent Bodies'. When large asteroids collide or hit planets and moons, they send enormous amounts of rock upwards. Some of these debris makes it to space where millions of years later it may wander into the path of the Earth and end up as a meteorite for us to pick up.

Formation & Evolution of Meteorites - Below is an image depicting the formation of meteorites. Towards the left you can see where chondrules were thought to have condensed and aggregated from the Solar Systems initial gas and dust cloud. During this time silicate material (stony) and iron material also separated. These aggregates cooled and formed larger Chondrite bodies. Later these were disrupted through impacts with each other and they remelted to form bodies from which Iron meteorites and Achondrites are thought to originate. Throughout all of these various processes, pieces manage to find their way to Earth for us to find as meteorites.

Click image to instantly enlarge the diagram in a new window.

Reprinted with permission of UNSW Press from 'Meteorites; A Journey Trough Space and Time' by Alex Bevan and John de Laeter.