J/ApJ/745/77 Photochemical model for planet WASP-12b (Kopparapu+, 2012)
A photochemical model for the carbon-rich planet WASP-12b.
Kopparapu R.K., Kasting J.F., Zahnle K.J.
<Astrophys. J., 745, 77 (2012)>
=2012ApJ...745...77K 2012ApJ...745...77K
ADC_Keywords: Models ; Planets
Keywords: planetary systems
Abstract:
The hot-Jupiter WASP-12b is a heavily irradiated exoplanet in a
short-period orbit around a G0-star with twice the metallicity of the
Sun. A recent thermochemical equilibrium analysis based on Spitzer and
ground-based infrared observations suggests that the presence of CH4
in its atmosphere and the lack of H2O features can only be explained
if the carbon-to-oxygen ratio in the planet's atmosphere is much
greater than the solar ratio ([C]/[O]=0.54). Here, we use a
one-dimensional photochemical model to study the effect of
disequilibrium chemistry on the observed abundances of H2O, CO,
CO2, and CH4 in the WASP-12b atmosphere. We consider two cases:
one with solar [C]/[O] and another with [C]/[O]=1.08. The solar case
predicts that H2 O and CO are more abundant than CO2 and CH4, as
expected, whereas the high [C]/[O] model shows that CO, C2H2, and
HCN are more abundant. This indicates that the extra carbon from the
high [C]/[O] model is in hydrocarbon species. H2 O photolysis is the
dominant disequilibrium mechanism that alters the chemistry at higher
altitudes in the solar [C]/[O] case, whereas photodissociation of
C2H2 and HCN is significant in the super-solar case. Furthermore,
our analysis indicates that C2H2 is the major absorber in the
atmosphere of WASP-12b and the absorption features detected near 1.6
and 8µm may be arising from C2H2 rather than CH4. The Hubble
Space Telescope's WFC3 can resolve this discrepancy, as C2H2 has
absorption between 1.51 and 1.54µm, while CH4 does not.
Objects:
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RA (2000) DE Designation(s)
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06 30 32.79 +29 40 20.3 WASP-12b = WASP-12b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 77 177 Reaction list and rate constants (K. Zahnle
2010, private communication) used in this study
refs.dat 267 41 References
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See also:
J/A+A/551/A108 : Multi-site obs. of WASP-12 b transit (Maciejewski+, 2013)
J/AJ/143/39 : Analysis of hot Jupiters in Kepler Q2 (Coughlin+, 2012)
J/A+A/528/A65 : WASP-12b transits (Maciejewski+, 2011)
J/ApJ/720/872 : A spectropolarimetric analysis of WASP-12 (Fossati+, 2010)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Num [1/166] Reaction number (1)
5- 9 A5 --- R1 Reactant 1 (among 31 chemical species)
11- 15 A5 --- R2 Reactant 2 (among 31 chemical species)
17 A1 --- R3 [M] Reactant 3 (among 31 chemical species)
20- 24 A5 --- P1 Product 1 (among 31 chemical species)
26- 30 A5 --- P2 Product 2 (among 31 chemical species)
32 A1 --- P3 [H/M] Product 3
34- 42 E9.3 --- K Rate: K coefficient (2)
44- 53 E10.3 --- a Rate: temperature exponent (2)
55- 64 E10.3 --- b Rate: exponential factor (2)
66- 67 A2 --- f_Ref [r-] r-: "reverse of" (2)
68- 77 A10 --- Ref Reference (see refs.dat file)
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Note (1): Only the forward rate constants are given as we calculate reverse
rate constants from the forward rate assuming thermodynamic equilibrium
(see discussion in Section 2). For three body reactions, the first and
second row represent the low and high pressure rate limits, respectively.
Note (2): The coefficients K, a and b represent the reaction rate expressed
as K.(T/298)a.exp(b/T) [K is given in cm3/s for 2-body reactions,
and cm6/s for 3-body reactions]. Only the "forward" reactions and
corresponding rate coefficients, kf, are given, from K. Zahnle
(2010, private communication). The reverse rate coefficients, kr, at
each temperature level (grid) were calculated assuming thermodynamic
equilibrium: kr=kf/keq, where keq is the equilibrium constant
for the reaction and is given by keq=exp(ΔG0/RT)
[ΔG0 is the change in the Gibbs free energy for the reaction].
See section 2 for the model description.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Code Reference code
8- 34 A27 --- Aut Author's name(s)
37- 40 I4 --- Year Year of publication
42-267 A226 --- Comm Title and reference of the publication
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 30-Jul-2013