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Terms and Characteristics
Meteoroids are stony or iron rocks that move through space. They can travel up to 26 miles per second in space. The Earth travels at 18 miles per second through space. Once the meteoroid enters the Earth's atmosphere, it is known as a meteor. If a meteoroid and Earth collide head-on, a meteor can move through the atmosphere at 44 miles per second. The intense friction with the atmosphere causes extreme heat. Meteors incinerate before they hit the surface. A meteorite is a meteor that has reached the surface before being completely vaporized.
Stony Meteorites
Stony meteorites are rich in silicon and oxygen. They may also have minimal amounts of iron and magnesium. Stony meteorites are dated to be about 4.55 billion years old, which is the age of the solar system. There are two types of stony meteorites: chondrites and achondrites. Chondrites are stony meteorites that may have broken off of planets or asteroids while the solar system was forming. Achondrites were broken off of an asteroid and were differentiated during their lifetime. Achondrites have gone through a melting and recrystallization phase similar to an igneous process. An achondrite has an iron-rich core surrounded by a silicon-rich crust.
Stony Iron Meteorites
Stony iron meteorites part iron and part silica. There are two major types: the pallasites and the mesosiderites. The pallasites are composed of an olivine core surrounded by an iron matrix. Mesosiderites are made up of breccia-like silicates, plagioclase and olivine. They are not separated into layers like pallasites. Mesosiderites' origin is thought to be through a collision of two asteroids which forced the inclusion of various materials.
Iron Meteorites
Iron meteorites are the most common found by collectors. They do not vaporize as easily on their journey through the atmosphere. Even though stony meteorites are much more common in earth strikes, iron meteorites have a high density and weather slowly, making them much more accessible to collectors. Their origin is from the asteroid belt and the outer solar system.
Meteor Showers
There are several debris field that the cross over the Earth's orbit. When the Earth passes through these debris fields, it experiences a meteor shower. The Perseid meteor shower occurs in August each year. The meteors appear to radiate out of the constellation Perseus. The Leonid meteor shower occurs in November each year. The Leonid shower is caused from the debris field of a passing comet.