Meteoroids that survive their journey through our atmosphere land on the Earth's surface as meteorites. They sometimes break up into several pieces while still in flight or when they hit the Earth. Large meteoroids can form brightly glowing fireballs (bolides) seen clearly in daylight, accompanied by spectacular light and sound effects. They can travel at very high speeds, typically from about 15 km - 70 km per second, the fastest ones (over 30 km per second) are destroyed on impact with the atmosphere. Most are heated for less than 10 seconds while they fall. Meteorites range in size from pea-sized pieces up to large masses many tonnes in weight.
Meteorites which are found after their fireball was witnessed are called 'falls', but if found accidentally long after their arrival they are called 'finds'. A famous Australian meteorite fall occurred on 28 September 1969 at Murchison, near Shepparton, Victoria. Meteorites are named after the locality where they have fallen (town, county, property, river, valley, mountain etc.).
About 500 tonnes of meteoritic debris falls to Earth every day, much of it as fine cosmic dust and micrometeorites that fall into the sea. About 500 meteorites of reasonable size would hit the Earth's surface every year, of which 150 would fall on dry land, and less than 10 would actually be found. Many fall in rugged, inaccessible landscapes and have a poor chance of being located. The largest known meteorite weighs 60 tonnes and still sits where it fell, at Hoba, Namibia.
Meteorites are extremely important to science, as they help us to better understand the origins and composition of the Solar System. They are our major source of extraterrestrial material apart from moon rocks retrieved by space missions.
Copyright © Australian Museum, 2004