Planetary Geoscience

We explain nucleosynthesis in evolving stars and use this foundation to understand the chemical composition of our own star and of the Solar System. Element abundances are determined from the Sun’s spectrum, and from laboratory measurements of the solar wind and chondritic meteorites. The metal-rich Solar System composition reflects the recycling of elements formed in earlier generations of stars. Condensation models of a cooling nebular gas having this composition produced the minerals found in refractory inclusions in chondrites. The deuterium enrichment in organic matter in chondrites suggests that hydrocarbons formed at low temperatures in molecular clouds and were subsequently processed into complex molecules in the solar nebula and in parent bodies. Ices condensed far from the Sun and were incorporated into the giant planets and comets. Element fractionations in the nebula were largely controlled by element volatility or by the physical sorting of solid grains. Separation of isotopes by mass was common in the nebula, although oxygen shows mass-independent fractionation.