1. Source of Atomic Hydrogen in the Atmosphere of HD 209458b Mao-Chang Liang Caltech Related publications 1. Liang et al. 2003, ApJ Letters, in press 2. Liang et al. 2003, manuscript in preparation

2. Outline Motivation of this Study Observation: Properties of HD 209458b Simulation: One-dimensional Model Results Summary

3. Motivation It is a Jupiter-size planet outside our solar system – relate to our solar system – how it formed/how it evolves HD 209458b is close-in, and is the best-studied – chemical processes? To be more specific, source of atomic hydrogen? – fuel hydrodynamic loss? – evolution of the atmosphere transit duration intensity star planet Roche lobe (Hill sphere) orbit not to scale

4. Observation of HD 209458 system The central star is a G0 solar-type dwarf star One giant planet found, HD 209458b It is nearly edge-on, ~85  inclination – facilitates detection of the atmosphere Physical parameters: 1.54 R J and 0.68 M J (gravity ~800 cm s -2 < g earth ) Orbital parameters: ~0.05 AU and 3.5 days period – probably tidally locked – permanent day/night – high UV flux/stellar irradiance: 10 4 of Jupiter – hot : > 1000 K

5. 1-D KINETICS model to simulate the chemical processes

6. Model description generating model atmosphere Model atmosphere calculated according to Seager et al. (2000) – Heating from stellar irradiance is uniformly distributed to the whole planet – Cloud-free and high temperature condensation-free – Temperature-Pressure-Altitude profile: radiative equilibrium + hydrostatic equilibrium – Chemical abundances: thermochemical equilibrium, using solar abundances (elements; reference model A) Eddy diffusion  n - ,  = 0.6-0.7

7. Model atmosphere

8. Simulation setup 253 chemical reactions involving C, H, and O Continuity of mass Solve for steady-state solution  0

9. Results H Production high H/H 2 ratio H 2 O + h  H + OH OH + H 2  H 2 O + H H 2 O Production CO + h  C + O O + H 2  OH + H OH + H 2  H 2 O + H UV-flux limited important for water-poor atmosphere CO H2OH2O H CO 2 CH 4

10. Summary OH and O radicals drive most of chemical reactions H 2 O plays as a catalyst in producing H H production is insensitive to the exact abundances of H 2 O, CO, and CH 4, as well as the eddy diffusion – H is 1000 times more than that of Jupiter – H formation is UV-flux limit H production timescale ~ 1 day ~ circulation time scale – importance of global circulation H mixing ratio > 1% at the top of atmosphere – fuel hydrodynamical loss? if escape parameter esc (  gravitational energy / thermal energy) < 10 End

12. Goukenleuque et al. 2000 0.46 M J, 0.05 AU, e ~ 0.013, G2

13. Generating model atmosphere Temperature-Pressure-Altitude profile: radiative transfer + radiative equilibrium + hydrostatic equilibrium Chemical abundances: thermochemical equilibrium, using solar abundances Iteration until the model is converged

14. Generating model atmosphere A table that contains T, P, and chemical abundances – minimizing Gibbs free energy Starting model atmosphere code – initial guess for T and P as a function of z Get chemical abundance from the table Calculate T and P as function of z Model converged New chemical abundances obtained Iteration until T, P, and chemical abundances converged

15. 1-D model technical detail mass continuity   n i /  t +  i /  z = P i  L i   I = -D i [  n i /  z + n i /H i + n(1+  i )/T  T/  z] -K[  n i /  z + n i /H a + n/T  T/  z]  H i and H a are scale heights for species i and atmosphere boundary conditions – lower boundary: initial abundances in the seep atmosphere, derived from thermochemical equilibrium – Upper boundary: zero flux for all species steady-state condition: time evolves until  0

16. Eddy diffusion determined from He distribution density-dependence (  n -  ) calculated from the upward-propagating gravity wave generated in the troposphere – from the constancy of energy density (e.g., n*u 2 =const) – constant below tropopause – exponential decay above tropopause

17. Timescales Radiative relaxation timescale of the atmosphere (c p /  T eff 3 ) – 1 day (~10 days on Earth, ~1000 days on Jupiter) Eddy diffusion transport timescale – greater than 10 6 sec at the bottom – less than 1000 sec at the top

18. Hydrodynamic loss Escape parameter: esc  (GM p m/r)/(kT)

19. Future Prospect Tidally locked – high wind speed, a few km/s  importance of global circulation  redistribute the produced species Temperature-pressure profiles – cloud distribution and high temperature condensation Haze/aerosol/hydrocarbon formation ( in preparation ) – affect optical spectra/albedo Observationally constrain the atmospheric abundance Effect of stellar wind Evolution of the produced H and planet itself Set constraints to see if planetary features can be detected in near future

20. Techniques – radial velocity – pulsar timing – eclipse/transit – astrometry First extrasolar planet, 51 Peg b, in 1995 First atmospheric detection, HD 209468b, in 2002 111 planets found so far (July of 2003) – Jupiter size – high eccentricity – close in – correlation of iron abundance with planetary formation Survey of extrasolar planets California & Carnegie Planet Search website http://exoplanets.org/ Debra Fishcer 2003

21. Determination of planet’s orbital and physical properties HD 209548 Mazeh et al. 2000 amplitude + period  Msin i + T orbit Charbonneau et al. 2000 duration + obscuration  R + i

22. Atmospheric features Sodium line Na D lines detected, ~4 sigma detection (2.32  0.57)  10 -4 Charbonneau et al. 2002

23. Atmospheric features Atomic hydrogen hydrogen in the atmosphere, – 15  4% detection larger than Roche lobe (?), 3.6 R J -> 10% maximum Vidal-Madjar et al. 2003 planet over exaggerated

24. Results H Production high H/H 2 ratio H 2 O + h  H + OH OH + H 2  H 2 O + H H 2 O Production CO + h  C + O O + H 2  OH + H OH + H 2  H 2 O + H CO 2 Production OH + CO  CO 2 + H CH 4 Production CO + h  C + O C + H 2 + M  3 CH 2 + M 2 3 CH 2  C 2 H 2 + 2H C 2 H 2 + H + M  C 2 H 3 + M C 2 H 3 + H 2  C 2 H 4 + H C 2 H 4 + H + M  C 2 H 5 + M C 2 H 5 + H  2CH 3 CH 3 + H + M  CH 4 + M UV-flux limited important for water-poor atmosphere source of hydrocarbons

25. Barman et al. (2002) T-P profiles

26. Fortney et al. (2003) T-P profiles

27. this work Barman et al. (2002) T-P profiles Fortney et al. (2003) T-P profiles

33. wavelength (angstrom) cross section (cm -2 )