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, USA2Research Center for Environmental Changes, Academia Sinica, Taiwan3University College London, UK.

Molecules in the Atmospheres of Extrasolar planetsParis, Nov 19-21, 2008

Start with colder planets

HD209458b H2O, CO, CO2, CH4 and hydrocarbons Sulfur species, Nitrogen species

Lessons from solar system

Today’s OutlineToday’s Outline

HD209458bHD209458b

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–

–

– Kzz = K0n-, 0.5

• Temperature profile from thermochemical calculation

• Chemical reactions from, for example, Yung and DeMore (1999)

iizzii

iatm

zz

i

iizzi

ii wn

T

KD

z

Tn

H

K

H

DnKD

z

n+

++∂∂

−+−+∂∂

−= ])1(

[)()(αϕ

iiii LPzt

n−=

∂∂

+∂∂ ϕ

Temperature profiles

Barman et al. 2002

Fortney et al. 2003

Seager et al. 2000

Jupiter

F/4

F/2F/2

Model atmosphere

Atomic Hydrogen

H Productionhigh H/H2 ratio

H2O + h H + OH OH + H2 H2O + H

Net: H2 + h 2H

H2O Production

CO + h C + OO + H2 OH + HOH + H2 H2O + H

Net: CO + 2H2 + h C + H2O + 2H

Hydrocarbons

CO + h C + OC + H2 + M 3CH2 + M2 3CH2 C2H2 + 2HC2H2 + H + M C2H3 + MC2H3 + H2 C2H4 + HC2H4 + H + M C2H5 + MC2H5 + H 2CH3

CH3 + H + M CH4 + M

CH4 Production

bottleneck

2[CO + h C + O]2[C + H2 + M 3CH2 + M] 3CH2 + 3CH2 C2H2 + 2HC2H2 + H + M C2H3 + MC2H3 + H2 C2H4 + HC2H4 + H + M C2H5 + MC2H5 + 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

N

NH3

HCN

CH3NH2

NO NH

CN

NH2

H2S

SH SS2

S3

SO

S4

S5

S6

S8

SO2

H2SO4

SO3

HSO

[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

OCSOCS

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.)

ConclusionsConclusions