Chemical Models of Terrestrial Exoplanets Bruce Fegley, Jr. and Laura Schaefer Planetary Chemistry Laboratory Department of Earth and Planetary Sciences McDonnell Center for the Space Sciences Washington University St. Louis, MO 63130 USA We use thermodynamic calculations to model atmospheric chemistry on terrestrial exoplanets that are hot enough for chemical equilibria between the atmosphere and lithosphere, as on Venus. The results of the calculations place constraints on abundances of spectroscopically observable gases, the surface temperature and pressure, and the mineralogy of the
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Chemical Models of Terrestrial Exoplanets Bruce Fegley, Jr. and Laura Schaefer Planetary Chemistry Laboratory Department of Earth and Planetary Sciences.
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Chemical Models of Terrestrial Exoplanets
Bruce Fegley, Jr. and Laura SchaeferPlanetary Chemistry LaboratoryDepartment of Earth and Planetary Sciences
McDonnell Center for the Space SciencesWashington UniversitySt. Louis, MO 63130
USA
We use thermodynamic calculations to model atmospheric chemistry on terrestrial exoplanets that are hot enough for chemical equilibria between the atmosphere and lithosphere, as on Venus. The results of the calculations place constraints on abundances of spectroscopically observable gases, the surface temperature and pressure, and the mineralogy of the planetary surface
Mineral Buffer Reactions• Co-existing minerals control (buffer) gas
partial pressures – single unique gas pressure at each temperature, e.g.
CaCO3 + SiO2 = CaSiO3 + CO2 (gas)
Calcite Quartz Wollastonite
log10 PCO2 = log10 Keq = 7.97 – 4456 / T
CQW Buffer for CO2
Venus - H2O buffer
KMg2Al3Si2O10(OH) 2 =
MgAl2O4 + MgSiO3 + KAlSiO4 + H2O
Eastonite – Spinel – Enstatite – Kalsilite log10 K = −0.782 + 78,856 / T