© David A. Kring
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Loss of material from the surface of a meteoroid being heated by friction as it passes through an atmosphere.
Process of particles sticking together to form larger bodies; for example, solar nebular dust accreted to form chondrules, and planetesimals accreted to form planets.
A stony meteorite representing differentiated planetary material. Because differentiation is an igneous process, these are igneous rocks or breccias of igneous rocks.
A fragment of a planetesimal (or possibly an aggregate of fragments). Most asteroids orbit the sun between Mars and Jupiter, although many also have orbits which cross that of the Earth and are thus called near-Earth asteroids (NEA's).
A rock consisting of many angular fragments, some of which may have different compositions.
A type of primitive chondrite with evidence of nebular processes.
A meteorite containing chondrules and other components produced in the solar nebula.
A rocky and icy body in orbit around the sun. These objects contain volatile material (such as hydrogen) which meteorites lack.
A bowl-like depression. On planetary surfaces, both volcanic craters and impact craters may exist, but because each type of crater has its own characteristics, scientists can determine whether a crater was produced by an impact or by volcanism.
Indicates a rock is composed of mineral crystals rather than glass. In general, when igneous melts cool very fast they form glass (like obsidian), but when they cool slower, mineral crystals have an opportunity to grow.
When a (partially) molten body has been divided into two or more fractions of dissimilar compositions. In the case of the Earth, iron-nickel metal was differentiated from silicate material to form the planet's core.
Material thrown out of a crater during an impact event.
A type of primitive chondrite that chondrite is dominated by the silicate mineral enstatite.
A meteorite that was observed to fall and recovered. Because this type of meteorite is usually collected soon after falling, weathering and other terrestrial processes do not have an opportunity to degrade the sample.
A meteorite that was not seen to fall, but found at some later date. For example, many finds from Antarctica fell 10,000 to 700,000 years ago.
A very large meteor.
A rock that was once molten.
A collision between two planetary bodies. In the case when one is much smaller than the other (like a meteoroid colliding with the Earth), a crater may be produced on the larger body.
impact melt spherule
Spherules of shock-melted rock ejected from an impact crater. Most of these objects cool rapidly in the Earth's atmosphere and solidify to a glassy state. However, some may remain molten until they splash onto the ground or into water where they are quenched to form solidified particles of glass.
Molten rock that is erupted onto the surface of a planet and is hot enough to flow.
Very hot, fluid rock. Magma is used to describe molten rock both below and on top of the surface of a planet and thus is a more general term than lava. Magma may contain solid mineral crystals which are suspended in the melt.
A type of stony-iron meteorite with silicate material and iron-nickel metal. These meteorites have been brecciated and metamorphosed, whereas pallasites, another type of stony-iron meteorite, are igneous rocks.
A rock that has been heated and compressed so that it recrystallizes, but does not melt.
A bright light produced when a meteoroid is frictionally ablated as it passes through an atmosphere. A very large and bright meteor is usually called a fireball.
A fragment of one planetary body that lands on another planetary body. In the case of Earth, a meteorite must survive ablation in the atmosphere.
A small (<1 km) natural object whose orbit around the sun may cause it to collide with other planetary bodies. The term meteoroid is usually used to describe the rocky core of a meteor, while the term meteorite is used to describe the object once it is on the ground.
A tiny particle from one planetary body which lands on another planetary body. Micrometeorites typically range in size from a millionth to a thousandth of a meter on Earth. Some micrometeoroids are melted or burned up completely in the Earth's atmosphere. On planetary bodies with much thinner atmospheres, such as the Moon, many more micrometeoroids survive.
A semi-spherical fragment of rock embedded in a matrix with a different composition.
The most common type of meteorite to fall on Earth. Some are primitive specimens containing evidence of nebular processes, while others have been metamorphosed on a planetary body.
A stony-iron meteorite in which nodules of olivine (a silicate mineral) are surrounded by a network of iron-nickel metal.
A rocky and/or icy body, a few to several tens of kilometers in size, that was produced in the solar nebula.
Unusually high pressures produced briefly by an impact. These pressures may be sufficiently high to shatter, melt, and vaporize rocky material.
Rocky material consisting, in part, of the elements silicon and oxygen. Most rocks on the surface of the Earth (such as sandstones, granites, rhyolites, and basalts) are silicate materials. (In contrast, metal that is separated from silicates during planetary differentiation lacks oxygen and contains very little, if any, silicon.)
The disk of gas and dust that surrounded the sun when it was forming.
A large area over which impact melt spherules or tektites are found.
Spherule of molten rock ejected from an impact crater and then cooled rapidly to produce glass.