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Equilibrium Chemistry of the Atmospheres of Hot Earth-like Exoplanets

Equilibrium Chemistry of the Atmospheres of Hot Earth-like Exoplanets

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Equilibrium Chemistry of the Atmospheres of Hot Earth-like Exoplanets

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  1. Equilibrium Chemistry of the Atmospheres of Hot Earth-like Exoplanets Laura Schaefer Katharina Lodders Bruce Fegley, Jr

  2. Introduction • Currently, there are several hundred known exoplanets • 24 super-Earths (M < 10MEarth) • Number of known exoplanets should go up considerably in February (Kepler releases data). • The Kepler and CoRot missions are dedicated space telescopes that are looking for transiting exoplanets • Some of the discovered exoplanets, such as CoRot-7b, are very hot • Here we report results for an Earth-like planet hot enough to vaporize its crust • Our results will be useful for spectroscopic studies of the atmospheres of hot super-Earths

  3. Methods • Chemical equilibrium calculations with a Gibbs energy minimization code • bulk system has abundances of the terrestrial continental crust • 1200 gases, 400 solid compounds included • T= 500 – 4000 K • P = 10-6 – 10+2.5 bars • Results here are for 100 bars unless otherwise stated

  4. Major Gas Chemistry Lithophiles Na, K, Fe, Mg, Si, Ti, Ca, Al Volatiles H, C, N, O, S

  5. Major Gas Chemistry • Molecular N2 is the major gas below ~500 K • From 500 – 3400 K, the major gas is H2O • CO2 is second most abundant gas • Molecular O2 is major gas from 3400 – 3900 K • At higher temperatures, SiO gas is the most abundant gas

  6. Major Gas Chemistry

  7. Major Gas Chemistry Lithophiles Na, K, Fe, Mg, Si, Ti, Ca, Al • Lithophile gases are dominated by Na and K below ~3600 K • Halides (F,Cl) + Hydroxides • Above ~3600 K, SiO and SiO2 are the most abundant lithophile gases

  8. Major Gas Chemistry

  9. Major Gas Chemistry

  10. Condensates • Graph shows the gas/condensed phase mole ratio for different total pressures • Higher ratio = more gas present • At high pressure, condensed phases persist to very high temperature

  11. Condensates • Graph shows the gas/condensed phase mole ratio for different total pressures • Higher ratio = more gas present • At high pressure, condensed phases persist to very high temperature • At low pressure, complete evaporation occurs at lower temperatures

  12. Summary • Continental crust produces an H2O + CO2 atmosphere over a broad temperature range at 100 bars • At very high temperatures O2 and SiO gas dominate • Alkali gases (e.g., KOH, KCl, NaOH, NaCl) are very abundant • In future work, we will explore differences in gas chemistry for a variety of interesting compositions • Oceanic crust, Bulk Silicate Earth, Moon, meteoritic compositions, etc. • Any requests?

  13. Major Gas Summary H2O OH CO2 CO N2 NO Volatiles H2O O2 SiO SO2 SiO2 SiO FAl(OH)2 Al(OH)3 FAlO AlO FeCl2 Fe(OH)2 FeO CaF2 CaFOH Ca(OH)2 Lithophiles NaCl NaOH Na Mg(OH)2 MgO KCl KOH K TiO2