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 < 10M Earth ) – 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 Continental Crust Composition Wedepohl (1995) ElementWt%ElementWt% O47.20Ti0.401 Si28.80C0.199 Al7.96P0.076 Fe4.32Mn0.072 Ca3.85S0.070 Na2.36F0.053 Mg2.20Cl0.047 K2.14H0.045

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

5. Major Gas Chemistry Molecular N 2 is the major gas below ~500 K From 500 – 3400 K, the major gas is H 2 O –CO 2 is second most abundant gas Molecular O 2 is major gas from 3400 – 3900 K At higher temperatures, SiO gas is the most abundant gas

6. Major Gas Chemistry ElementMajor Gases HH 2 O (300 – 3950 K) OH (3950 – 4000 K) CCO 2 (300 – 3950 K) CO (3950 – 4000 K ) NN 2 (300 – 2850 K) NO (2850 – 4000 K) OH 2 O (300 – 3400 K) O 2 (3400 – 3950 K) SiO (3950 – 4000 K) SSO 2 (300 – 4000 K)

7. Major Gas Chemistry Lithophile gases are dominated by Na and K below ~3600 K –Halides (F,Cl) + Hydroxides Above ~3600 K, SiO and SiO 2 are the most abundant lithophile gases Lithophiles Na, K, Fe, Mg, Si, Ti, Ca, Al

8. Major Gas Chemistry ElementMajor Gas SiSiO 2 (500-3350 K) SiO (3350-4000 K) FeFeCl 2 (500 – 1900 K) Fe(OH) 2 (1900 – 3650 K) FeO (3650 – 4000 K) NaNaCl (500 – 2900 K) NaOH (2900 – 3700 K) Na (3700 – 4000 K) MgMg(OH) 2 (500 – 3650 K) MgO (3650 – 4000 K) KKCl (500 – 2750 K) KOH (2750 – 3950 K) K (3950 – 4000 K)

9. Major Gas Chemistry ElementMajor Gas TiTiO 2 (500 – 4000 K) Al (X i < 10 -3 ) FAl(OH) 2 (300-2600 K) Al(OH) 3 (2600 – 3200 K) FAlO (3200 – 3950 K) AlO (3950 – 4000 K) Ca (X i < 10 -5 ) CaF 2 (500 – 2200 K) CaFOH (2200 – 3050 K) Ca(OH) 2 (3050 – 4000 K)

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 % of element in gas at 4000 K, 100 bars Na11.2% K49.7% Fe4.5% Mg1.3% Al0.3% Ca~0% Ti38.7% Si9.8%

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 Temperature of 100% evaporation P = 10 -6 bars Na1550 K K Fe1700 K Mg1850 K Al2200 K Ca2150 K Ti1800 K Si2000 K

12. Summary Continental crust produces an H 2 O + CO 2 atmosphere over a broad temperature range at 100 bars At very high temperatures O 2 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 H2OH2O CO 2 N2N2 NO H2OH2OO2O2 SO 2 SiO 2 SiO FAl(OH) 2 Al(OH) 3 FAlO FeCl 2 Fe(OH) 2 FeO CaF 2 CaFOHCa(OH) 2 NaClNaOHNa Mg(OH) 2 MgO KClKOH TiO 2 OH CO SiO AlO K Volatiles Lithophiles