What are meteorites?
Meteorites are rocks from Space which enter the Earth’s atmosphere and don’t completely burn up before landing on the surface. All meteorites come from within our Solar System. The vast majority of meteorites are rocky fragments from the asteroid belt, between the orbits of Jupiter and Mars. Radiometric dating shows nearly all meteorites formed about 4 500 million years ago, at the same time as the Solar System, including Earth. A few meteorites from Mars are younger. There are also meteorites derived from the Moon.
Two specimens of the Murchison meteorite which fell at Murchison, 80 km north of Melbourne, on the 29 September 1969. Murchison is a rare type of meteorite classified as a carbonaceous chondrite. Also featured, is a perfect flanged australite button from Port Campbell.
Photographer: Frank Coffa / Source: Museum Victoria
What effects does a meteorite have on Earth?
Meteorites have been colliding with Earth since it formed. There have been many very large impacts in that time. Some of these may have caused major extinction of many life forms. The remains of several hundred very large meteorite impact craters can be seen today on very old parts of the Earth’s crust. In Australia, there are about 25 impact craters preserved.
Meteorites enter the Earth’s atmosphere travelling at more than 11 km per second. Frictional heating causes a fireball in the upper atmosphere. Small meteorites may burn up and large loosely bound meteorites may break up. Sonic booms and strange whistling, humming or crackling sounds may occur.
Meteorites can fall anywhere on Earth. Those falling into the oceans or in forests are hardly ever found. Meteorites seen to fall and collected immediately are known as falls; those found long afterwards are known as finds. Like all rocks, meteorites begin to weather on the surface due to reaction with water and oxygen. Eventually they break down and disappear into the soil.
How do you identify and classify meteorites?
Meteorites consist mainly of common minerals which are also found in rocks on Earth. However the proportions of these minerals, and the textures they form, are different to rocks found in the Earth’s crust. Sophisticated chemical comparisons must be made in order to identify Martian or Lunar meteorites. Meteorites are divided into three broad groups, stony, iron and stony-iron. Stony meteorites containing millimetre-sized spheres known as chondrules are called chondrites; those without are called achondrites. Within these broad groups there are many different classes of meteorites.
A meteorite name is chosen which is based on the nearest named location to where the meteorite was found. The data and name are sent to an international committee for appraisal. If they are approved, the meteorite is entered in an international catalogue.
Meteorites have great scientific interest, as they provide us with clues on the origin of the Solar System, as well as of planets like Earth. They also have a monetary value, as there are many meteorite collectors around the world who buy and trade meteorites.
Are meteorites protected?
Federal laws protect meteorites found in Australia and it is an offence to export one without a permit. In Western Australia and South Australia legislation means that meteorites are the property of the Government and must be lodged with an appropriate Museum. In other States, the finder is able to keep a meteorite.