Planetary differentiation solar system composition

The Earth and other planetary bodies have been heavily modified by planetary-scale differentiation, smaller scale melting and the resulting chemical fractionations, collisions that mix material with different histories, and other processes. Samples of these materials are thus not suitable for determining the solar system composition. More primitive objects, such as comets and chondritic meteorites, have compositions more similar to the composition of... 

Many meteorites have never been subjected to processes of planetary differentiation. These imdifferentiated meteorites come fix>m planetesimals that were never molten and resemble die composition of the solar nebula at the time and place of their formation. They exhibit approximately solar system composition, are called chondritic meteorites, and represent one big group of meteorites. The second group consists of the differentiated meteorites which represent pieces of partially or totally molten parent bodies. Examples of this group are meteoritic basalts (eucrites) or iron meteorites. The latter are pieces of the segregated core of the parent body. 

Some meteorites, and all planetary samples, have undergone melting and differentiation at some stage. Hence, the compositions of differentiated materials do not resemble solar system abundances. These samples can, however, tell us about various geochemical processes within asteroids and planets. 

Cosmochemislry places important constraints on models for the origin of the solar nebula and the formation and evolution of planets. We explore nebula constraints by defining the thermal conditions under which meteorite components formed and examine the isotopic evidence for interaction of the nebula with the ISM and a nearby supernova. We consider how planetary bulk compositions are estimated and how they are used to understand the formation of the terrestrial and giant planets from nebular materials. We review the differentiation of planets, focusing especially on the Earth. We also consider how orbital and collisional evolution has redistributed materials formed in different thermal and compositional regimes within the solar system. 

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