Meteorites are bits of the solar system that fall onto the earth surface. They are origins of the outer space that withstand the collision from the surface of our planet. When in the outer space, they are known as meteoroids. Once they enter the earth surface, they are called meteors. A meteor or meteorite is a bright streak of light in the sky, popularly known as the shooting star or falling star, which is produced by the entry of a small meteoroid into the earth's atmosphere. A meteorite is common on the surface of a celestial body and has been noted on moon and mars as well.
Meteorites that are found after being watched at the time they enter the atmosphere or the earth are known as falls, while the rest of the meteorites are known as finds. The count of meteorites that have been recognized has reached to more than thousand. Approximately 1,050 witnessed falls have specimens in the world’s collections, as per the data records available till mid-2006. In a stark contrast to this, over 31,000 well-documented meteorite finds exist. Meteorites are usually named after the place where they are found. The name is based either on the name of the nearby town or a geographic landmark situated closely. The recovered mass of meteorite is a rarest specimen found on earth and gives a clue as to how the planet's surface came to be made.
Types of Meteorites
Meteorites or meteors are generally classified into three types - stony meteorites, iron meteorites and stony-iron meteorites.
Stone meteorites can be further classified into two groups: chondrites and achondrites. They are made of silicate materials. The form of most of the chondrites has remained unchanged ever since their formation, which was some 4.56 billion years ago, almost following the formation of sun. Small, gaseous, spherical inclusions that formed during the solar nebula, which can be described as chondrules, are contained by almost all chondrites. Achondrites were seemingly chondrites in the beginning, but their form was later altered by heating or a big impact event. These meteorites are less common than chondrites and include the HED group from asteroid 4 Vesta and SNCs from the planet Mars.
Iron meteorites are believed to be the pieces of broken cores of differentiated asteroids, containing varying amounts of nickel and iron. These meteorites comprise the three basic groups: Hexahedrites - containing 4.5 to 6.5 percent nickel; Octahedrites - containing 6.5 to 13 percent nickel; and Ataxites - containing 16 to 30 percent nickel. On the basis of weight, iron meteorites are the most common meteorites group.
Stony Iron Meteorites
The stony-iron meteorites can be classified into two groups: Mesosiderites and Pallasites. Mesosiderites are formed bybroken angular fragments of mantle rock and nickel-iron, fused with each other by impacts with another body. Pallasites are believed to be some of the most attractive meteorites. They are formed at the core mantle boundary of asteroids. Crystals of olivine are present in these meteorites.