Meteorites are pieces of space debris which, having survived a fiery journey through the atmosphere, land on the earth’s surface. They provide much of our knowledge of the origin and evolution of the solar system. Apart from a few kilograms of rock brought back from the moon by astronauts, meteorites are the only material from beyond the earth available for study.
Meteoroid, meteor or meteorite?
A meteoroid is a piece of rock or space debris in our solar system. If it enters the earth’s atmosphere, it becomes visible as a meteor – a bright, moving trail of light, commonly called a ‘shooting star’.
If the object survives its blazing plunge through the atmosphere and lands on the surface of the earth, it is called a meteorite.
What are meteorites made of?
Meteorites are divided into two groups: stony meteorites (stones) and iron meteorites (irons).
Stony meteorites are the most common, and are composed of silicate minerals, similar to volcanic rocks found on earth. Many contain tiny spheres (chondrules), which have been formed by the rapid cooling and solidification of molten droplets. These distinctive stony meteorites are known as chondrites (pronounced ‘kon-drites’). Their chemical composition closely matches that of the sun.
Iron meteorites are heavy and look different from normal rocks, so they tend to be picked out as unusual. They resist weathering, although they are often rusty on the outside. Most iron meteorites contain 7–15% nickel. The curious and distinctive markings revealed by cutting and etching are intergrowths of metal crystals called Widmanstatten structures.
Falls and finds
Meteorites that have been observed landing are classified as falls; those which have been discovered later, on or beneath the earth’s surface, are called finds. Thousands of meteorites land on earth every year, but only five or six are ever found. Meteorites are named after the place where they are found.