is a fragment of rock or iron from outer space, usually a meteoroid or asteroid, which survives passage through the atmosphere as a meteor to impact the surface of the Earth. Meteorites
are believed to originate in the asteroid belt between the planets of Mars and Jupiter. A meteorite may range in size from less than a gram to more than 60 tons.
When the path of these space rocks intersects with Earth's orbit, the meteoroid enters the atmosphere at high velocity causing the luminous phenomena we call a meteor or shooting star. These meteors should not be confused with a meteor shower
. Meteor showers involve the Earth passing through a comets orbit.
A very bright meteor is called a fireball and may be called a bolide if associated with a smoke train and detonations (which often produces meteorites). These events can also be tremendous force of nature. The recent Russian meteor
sonic boom and shock wave on February 15, 2013 caused considerable property damage and injury to people.
Sometimes the forces on these objects are too great and fragmentation will occur resulting in a few to even many thousands of individual pieces. The area on the ground surface meteorites cover is a distribution ellipse also know as a strewnfield.
As the meteoroid passes through the atmosphere, ablation occurs where melting and vaporization removes material from the surface. This ablation can also produce regmaglyphs which are flight marks produced during the passage of a meteoroid through the atmosphere and often look like thumbprints pushed into the surface. This melting of the exterior surface from heating due to it's high velocity through Earth's atmosphere is also what causes the fusion crust seen on the exterior of meteorites. These factors help us with meteorite identification
because the exterior features of space rocks are different from that of Earth rocks.
An oriented meteorite is formed when it's passage through the atmosphere is in a stable orientation. It receives the characteristic ablation features from being melted mostly on one surface. Among these features are a rounded front surface or a cone shape and often radial lines of melting in the front surface, and a rolled over lip of melted material which has cooled around the circumference of the back side.
On very rare occasions large meteoroids will reach the ground with enough velocity and mass to form an impact crater. The best preserved impact crater today is Meteor Crater in Arizona
. Associated with impact structures and craters is a type of rock called an impactite. This glassy rock, also called crater glass, is formed from the melting of native rocks during the impact of asteroids. A second glassy object associated with impact events but much less understood are tektites. A tektite
is a natural glass object formed by the melting of native rocks during some asteroid impacts. Some tektites, the Australites, receive aerodynamic shapes as the still plastic but cooling glass falls back to the surface from very high altitude. Muong Nong tektite glass may be from a melt sheet formed near the impact site.
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