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

Abstract

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 (1500–2500 K). Finally, our results may be useful for interpreting spectroscopic observations of accreting extrasolar terrestrial planets.