Agglomeration of planetesimals and planets

The formation of the terrestrial planets is constrained by their bulk chemical compositions, but determining the compositions of entire planets is challenging. Because planets are differentiated into crust, mantle, and core, there is no place on or within a planet that has the composition of the entire body. Before considering the formation of the terrestrial planets, let s review how we go about estimating their bulk compositions. 

Element Abundance Element Abundance Element Abundance 

In estimating the bulk compositions of the other terrestrial planets, there are not nearly so many constraints. Determination of a planet s mass (obtained from its gravitational effect on the orbits of moons or nearby spacecraft) and volume (calculated from its diameter as measured by telescopes) enables the calculation of its mean density. A meaningful comparison of planet mean densities requires that we correct for the effects of self-compression due 

Uncompressed mean densities of the terrestrial planets and the Moon (Taylor and McLennan, 2009) vary with the relative volume proportions of cores and mantles. 

Mass fractions of cores (metallic iron) versus concentrations of FeO in mantles (oxidized iron) in the terrestrial planets and asteroid Vesta. After Righter et al. (2006). 

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