Mapping the nebular condensates and the chemical composition of the terrestrial planets

- Thermodynamics of nebular condensates provide compositions of terrestrial planets.
- Solids suitable for Mercury formed around 1530 K and a nebular pressure of 0.001 bar.
- Solids suitable for Earth, Venus and Mars around 600 K and a pressure of 0.0001 bar.
- A suitable pressure-temperature nebular space for carbon precipitation is mapped.
- Oxygen fugacity in the nebula and the formation of iron oxide is discussed.

We demonstrate that the condensation theory of planet formation yields solids of suitable compositions in the solar nebula that accrete to form the terrestrial planetary bodies. The mineral chemistry of the condensed objects provides definite criteria to establish the pressure and temperature of their formation. The solids condensing at a high nebular pressure of 0.01 to 0.001 bar and temperature of ∼1530 K had the best chemical composition and density to form Mercury (64 wt% iron and 36 wt% oxides, density ∼5.32gcm3). Solids that condensed around a pressure of 0.0001 bar or less and a temperature of ∼700 K formed Earth and Venus (31 wt% iron, Ni and S and 69 wt% oxides, density ∼4 gcm3), and Mars (33.6 wt% Fe and S and 66.4 wt% oxides, density ∼3.7 gcm3). Iron sulfide provided S (3 wt%) for the core. Hydrous minerals forming in the lower temperature region provided water to the mantle. These results are highly significant because we have used only the chemical composition of the solar nebula, thermochemistry and astrophysical data on densities of the planets.