Iron meteorites are thought to be mostly derived from cores of differentiated planetesimals: a few likely formed from smaller metallic pools in the mantle or crust.Ĭhondrites are divided into three major classes called enstatite, ordinary, and carbonaceous, which are subdivided into 13 groups. Differentiated meteorites formed from chondritic planetesimals that melted, enabling sulfur-rich metal to sink forming metallic cores surrounded by silicate mantles and crusts. They formed in the protoplanetary disk, or solar nebula, by accretion of grains of metallic iron-nickel, sulfide, silicate, once molten, millimeter-sized spherules called chondrules, and refractory materials, including calcium- and aluminum-rich inclusions (CAIs). Chondrites have bulk chemical compositions like that of the Sun, neglecting the highly volatile elements like hydrogen, carbon, and nitrogen. There are two basic kinds of meteorite: chondrites and differentiated, or non-chondritic, meteorites (Hutchison, 2004 Krot, Keil, Scott, Goodrich, & Weisberg, 2014 Norton, 2002 also see “ Meteorites”). Iron meteorites therefore contain important clues to the formation of planetesimals that melted and they also provide constraints on theories for the formation of planets and asteroids. Some may have formed beyond Jupiter others show isotopic similarities to Earth and may have formed in the neighborhood of the terrestrial planets. Although iron meteorites are derived from asteroids, their isotopic anomalies provide the best clues that some come from planetesimals that did not form in the asteroid belt. Isotopic analysis also shows that iron meteorites, like other meteorite types, display small anomalies due to pre-solar grains that were not homogenized in the solar nebula (or protoplanetary disk). Bodies that accreted more than ~2 million years after the oldest known solids (refractory inclusions in chondrites) should not have contained enough 26Al to melt. Their unexpected antiquity is consistent with 26Al heating of planetesimals. Isotopic dating suggests that the parent bodies of iron meteorites formed before those of chondrites, and some irons appear to be the oldest known meteorites. Isotopic analysis provides formation ages for iron meteorites and clues to their provenance. The other three groups are richer in silicates and probably come from pools of molten metal in chondritic bodies. Chemical variations within all but three groups are consistent with fractional crystallization of molten cores of planetesimals. 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.

Non magnetic meteorite