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A solid natural object reaching a planet’s surface from interplanetary space.
Solid portion of a meteoroidSmall rocky or metallic object in orbit around the Sun (or another star). that survives its fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If Click on Term to Read More to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and textures. Meteorites range in size from microscopic to many meters across. Of the several 10s of tons of cosmic material entering Earth’s atmosphere each day, only about one ton reaches the surface.
Heating begins at an altitude of 100-120 km when a meteoroid encounters the Earth’s atmosphere. An object’s chance of survival depends on its initial mass, speed and angle of entry, and friability (tendency to break up). Micrometeoroids radiate heat so effectively that they are dramatically slowed without being vaporized and fall as a continuous, gentle, invisible rain. Meteoroids with masses between 10-6g and 1 kg tend to burn up completely as meteors. Friable meteoroids break up and are destroyed at altitudes of 80 to 90 km. Those which are tougher survive longer and produce fireballs as their surface undergo melting and ablationGradual removal of the successive surface layers of a material through various processes. • The gradual removal and loss of meteoritic material by heating and vaporization as the meteoroid experiences frictional melting during its passage through the atmosphere. The resulting plasma ablates the meteor and, in cases where a meteor Click on Term to Read More at temperatures of several thousand degrees. If meteoroids avoid destruction high up, they enter the lower, denser part of the atmosphere where they are rapidly decelerated. Finally, at subsonic speeds the fireballA fireball is another term for a very bright meteor, generally brighter than magnitude -4, which is about the same magnitude of the planet Venus as seen in the morning or evening sky. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation. Click on Term to Read More is extinguished and what remains falls to the ground as a meteorite. The last melted material on the surface of the object solidifies to form a thin, usually black, rind known as a fusion crustMelted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of 4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below. Click on Term to Read More.
A natural solid object larger than 10 μm in size that was ejected by the impacts between meteoroids and/or larger natural bodies, was then transported by natural means from the body from which it was ejected to a region outside the dominant gravitational influence of that body, and later, when their orbits intersected, collided with a natural or artificial body larger than itself (even if it is the same body from which it was launched). Meteorites found on Earth, or any planetThe term "planet" originally comes from the Greek word for "wanderer" since these objects were seen to move in the sky independently from the background of fixed stars that moved together through the seasons. The IAU last defined the term planet in 2006, however the new definition has remained controversial. Click on Term to Read More with a sufficiently dense gaseous atmosphere, will have experienced ablation due to frictional forces experienced during the object’s high velocity entry through the planet’s atmosphere. An object loses its status as a meteorite if it is incorporated into a larger rock that itself becomes a meteorite at a later time (xenoliths found in meteorites are one example).
Weathering processes do not affect an object’s status as a meteorite as long as something recognizable remains of its original minerals or structure. These highly altered materials that have a meteoritic origin but are dominantly (>95%) composed of secondary mineralsMineral that forms through processes such as weathering, and in the case of meteorites can also include pre-terrestrial alteration. Secondary minerals in meteorites that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic Fe-Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by Click on Term to Read More formed on the body on which the object was found are called Relict Meteorites. (Meteoritical Society, 2006)