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Equilibrium Chemistry of the Atmospheres of Hot Earth-like Exoplanets Laura Schaefer Katharina...
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Transcript of Equilibrium Chemistry of the Atmospheres of Hot Earth-like Exoplanets Laura Schaefer Katharina...
Equilibrium Chemistry of the Atmospheres of Hot Earth-like
Exoplanets
Laura SchaeferKatharina LoddersBruce Fegley, Jr
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
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 CompositionWedepohl (1995)
Element Wt% Element Wt%
O 47.20 Ti 0.401
Si 28.80 C 0.199
Al 7.96 P 0.076
Fe 4.32 Mn 0.072
Ca 3.85 S 0.070
Na 2.36 F 0.053
Mg 2.20 Cl 0.047
K 2.14 H 0.045
Major Gas ChemistryVolatilesH, C, N, O, S
LithophilesNa, K, Fe, Mg, Si, Ti, Ca, Al
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
Major Gas ChemistryElement Major Gases
H H2O (300 – 3950 K)
OH (3950 – 4000 K)
C CO2 (300 – 3950 K)
CO (3950 – 4000 K )
N N2 (300 – 2850 K)
NO (2850 – 4000 K)
O H2O (300 – 3400 K)
O2 (3400 – 3950 K)
SiO (3950 – 4000 K)
S SO2 (300 – 4000 K)
Major Gas Chemistry
• 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
LithophilesNa, K, Fe, Mg, Si, Ti, Ca, Al
Major Gas ChemistryElement Major Gas
Si SiO2 (500-3350 K)
SiO (3350-4000 K)
Fe FeCl2 (500 – 1900 K)
Fe(OH)2 (1900 – 3650 K)
FeO (3650 – 4000 K)
Na NaCl (500 – 2900 K)
NaOH (2900 – 3700 K)
Na (3700 – 4000 K)
Mg Mg(OH)2 (500 – 3650 K)
MgO (3650 – 4000 K)
K KCl (500 – 2750 K)
KOH (2750 – 3950 K)
K (3950 – 4000 K)
Major Gas ChemistryElement Major Gas
Ti TiO2 (500 – 4000 K)
Al
(Xi < 10-3)
FAl(OH)2 (300-2600 K)
Al(OH)3 (2600 – 3200 K)
FAlO (3200 – 3950 K)
AlO (3950 – 4000 K)
Ca
(Xi < 10-5)
CaF2 (500 – 2200 K)
CaFOH (2200 – 3050 K)
Ca(OH)2 (3050 – 4000 K)
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
Na 11.2%
K 49.7%
Fe 4.5%
Mg 1.3%
Al 0.3%
Ca ~0%
Ti 38.7%
Si 9.8%
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
Na 1550 K
K 1550 K
Fe 1700 K
Mg 1850 K
Al 2200 K
Ca 2150 K
Ti 1800 K
Si 2000 K
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?
Major Gas SummaryH2O
CO2
N2 NO
H2O O2
SO2
SiO2 SiO
FAl(OH)2 Al(OH)3 FAlO
FeCl2 Fe(OH)2 FeO
CaF2 CaFOH Ca(OH)2
NaCl NaOH Na
Mg(OH)2 MgO
KCl KOH
TiO2
OH
CO
SiO
AlO
K
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