Chemical analysis show that most iron meteorites can be divided into 14 groups: about 15% appear to come from another 50 or more poorly sampled parent bodies. Impact processes were also important in the creation of many iron meteorites when planetesimals were molten. However, a few iron meteorites probably formed by impact melting of chondritic material. The major heat source for melting planetesimals was the radioactive isotope 26Al, which has a half-life of 0.7 million years. They provide important evidence for impacts between molten or partly molten planetesimals. A few percent of iron meteorites also contain silicate inclusions, which should have readily separated from molten metal because of their buoyancy. Melting in planetesimals caused dense metal to sink through silicate so that metallic cores formed.Ī typical iron meteorite contains 5–10% nickel, ~0.5% cobalt, 0.1–0.5% phosphorus, 0.1–1% sulfur and over 20 other elements in trace amounts. These bodies, called planetesimals, were composed of mixtures of grains of silicates, metallic iron-nickel, and iron sulfide with compositions and proportions like those in chondrite meteorites. The chemical compositions of iron meteorites generally match those predicted from experimental and theoretical considerations of melting in small bodies. Their great diversity offers remarkable insights into the formation of asteroids and the early history of the solar system. Iron meteorites are thought to be samples of metallic cores and pools that formed in diverse small planetary bodies. Destruction of Iron Meteorite Parent Bodies.Is Achondritic Material Present in Ordinary Chondrites?.Remanent Magnetization in Chondrites: Evidence for a Core Dynamo?.Did Iron Meteorite Parent Bodies Have Chondritic Surfaces?.Accretion of Iron Meteorite Parent Bodies.When Did Asteroids Form Metallic Cores?.Why Did Some Asteroids Melt to Form Metallic Bodies?.Crystallization and Chemical Trends Within Groups.Shock, Deformation, Impact Heating and Melting.Thermal Histories Inferred From Microstructure.Massive Minerals That Crystallized From Molten Metal.
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