Chemistry of atmospheres formed during accretion of the Earth and other terrestrial planets

摘要

We used chemical equilibrium and chemical kinetic calculations to model chemistry of the volatiles released by heating different types of carbonaceous, ordinary and enstatite chondritic material as a function of temperature and pressure. Our results predict the composition of atmospheres formed by outgassing during accretion of the Earth and other terrestrial planets. Outgassing of CI and CM carbonaceous chondritic material produces H_2O-rich (steam) atmospheres in agreement with the results of impact experiments. However, outgassing of other types of chondritic material produces atmospheres dominated by other gases. Outgassing of ordinary (H, L, LL) and high iron enstatite (EH) chondritic material yields H_2-rich atmospheres with CO and H_2O being the second and third most abundant gases. Outgassing of low iron enstatite (EL) chondritic material gives a CO-rich atmosphere with H_2, CO_2, and H_2O being the next most abundant gases. Outgassing of CV carbonaceous chondritic material gives a CO_2-rich atmosphere with H_2O being the second most abundant gas. Our results predict that the atmospheres formed during accretion of the Earth and Mars were probably H_2-rich unless the accreted material was dominantly CI and CM carbonaceous chondritic material. We also predict significant amounts of S, P, Cl, F, Na, and K in accretionary atmospheres at high temperatures (1500-2500K). Finally, our results may be useful for interpreting spectroscopic observations of accreting extrasolar terrestrial planets.