Photochemistry in the Atmospheres of
Hot Jupiters
Yuk L. Yung1, Mao-Chang Liang2, Michael Line1 and Giovanna Tinetti3
1Division
of Geological and Planetary Sciences, California Institute of Technology, USA
2Research Center for Environmental Changes, Academia Sinica, Taiwan
3University College London, UK.
Molecules in the Atmospheres of Extrasolar planets
Paris, Nov 19-21, 2008
Today’s Outline
 Start
with colder planets
 HD209458b
 H2O,
CO, CO2, CH4 and hydrocarbons
 Sulfur species, Nitrogen species
 Lessons
from solar system
HD209458b
Chemical processes
• Chemical composition different from that
of Jupiter
– CO and H2O are abundant; CH4 not abundant
• UV radiation a lot more enhanced
– Can break up more molecules
– Boost subsequent chemical reactions
• Performing photochemical calculation for
HD 209458b
Properties of HD 209458b
• “Best known” planet
– First discovered transiting planet (Henry et al. 2000)
– First atmosphere detection (Charbonneau et al. 2001)
– First exosphere detection (Vidal-Madjar et al. 2003)
• Orbiting HD 209458 G0V-type star
– ~0.05 AU or 3.5 days
• Inclination angle ~85
• Radius 1.54 RJ and mass 0.68 MJ
One-dimensional photochemical
model
• Solving mass continuity equation
–
–
ni  i

 Pi  Li
t
z
i

ni
D
K
T (1   i ) Di  K zz
( Di  K zz )  ni ( i  zz )  ni
[
]  ni wi
z
H i H atm
z
T
– Kzz = K0n-,   0.5
• Temperature profile from thermochemical
calculation
• Chemical reactions from, for example, Yung and
DeMore (1999)
Temperature profiles
Barman et al. 2002
Fortney et al. 2003
F/2
Jupiter
F/2
F/4
Seager et al. 2000
Model atmosphere
Atomic Hydrogen
H2O Production
CO + h  C + O
O + H2  OH + H
OH + H2  H2O + H
Net: CO + 2H2 + h 
C + H2O + 2H
H Production
high H/H2 ratio
H2O + h  H + OH
OH + H2  H2O + H
Net: H2 + h  2H
Hydrocarbons
CH4 Production
CO + h  C + O
C + H2 + M  3CH2 + M
2 3CH2  C2H2 + 2H
C2H2 + H + M  C2H3 + M
C2H3 + H2  C2H4 + H bottleneck
C2H4 + H + M  C2H5 + M
C2H5 + H  2CH3
CH3 + H + M  CH4 + M
2[CO + h  C + O]
2[C + H2 + M  3CH2 + M]
3CH + 3CH  C H + 2H
2
2
2 2
C2H2 + H + M  C2H3 + M
C2H3 + H2  C2H4 + H
C2H4 + H + M  C2H5 + M
C2H5 + H  2CH3
2[ CH3 + H + M  CH4 + M]
2[ O + H2  OH + H]
2[ OH + H2  H2O + H]
2[ H + H + M  H2 + M]
net
2CO + 3H2  CH4 + 2H2O
N2
HCN
NH3
NH2
CH3NH2
N
CN
NO
NH
S2
SH
S
H2S
SO
HSO
S3
SO3
S5
S6
S8
S4
SO2
H2SO4
[Friedson et al., Icarus, 2002]
Conclusions
Common photochemistry: hundreds of molecules, thousands
of reactions
Similar Processes: Catalytic cycles, evolution, hydrodynamic
escape, thermal inversion
Advice to modelers:
Dans ce meilleur des mondes possibles … tout est au mieux.
(In this best of possible worlds … all is for the best.)
Advice to observers:
Dieu n’est par pour les gros bataillons, mais pour ceux qui
tirent le mieux.
(God is on the side not of the heavy battalions, but of the
best shots.)
Acknowledgements
• NASA and ESA
• Yung’s Group at Caltech
• Liang Ph.D. Thesis 2005
• Meadows et al. 2008
• Yung and DeMore (1999) Book
Back-up slides
OCS
OCS
Conclusions

Common photochemistry: hundreds of molecules, thousands of
reactions

Similar Processes: Catalytic cycles, evolution, hydrodynamic escape,
thermal inversion

Advice to modelers:
Dans ce meilleur des mondes possibles … tout est au mieux
(In this best of possible worlds … all is for the best.)

Advice to observers:
Dieu n’est par pour les gros bataillons, mais pour ceux qui tirent le
mieux.
(God is on the side not of the heavy battalions, but of the best shots.)