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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 Outline Motivation of this Study Observation: Properties of HD 209458b Simulation: One-dimensional Model Results Summary Motivation to scale not It is a Jupiter-size star planet outside our solar system intensity – relate to our solar system planet orbit – how it formed/how it evolves Roche lobe (Hill sphere) HD 209458b is close-in, and is the best-studied transitprocesses? duration – chemical To be more specific, source of atomic hydrogen? – fuel hydrodynamic loss? – evolution of the atmosphere 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 RJ and 0.68 MJ (gravity ~800 cm s-2 < gearth) Orbital parameters: ~0.05 AU and 3.5 days period – – – – probably tidally locked permanent day/night high UV flux/stellar irradiance: 104 of Jupiter hot : > 1000 K 1-D KINETICS model to simulate the chemical processes 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 Model atmosphere Simulation setup 253 chemical reactions involving C, H, and O Continuity of mass Solve for steady-state solution • <ni/t> 0 Results H Production high H/H2 ratio H2O + h H + OH OH + H2 H2O + H UV-flux limited H2O Production CO + h C + O O + H2 OH + H OH + H2 H2O + H H CO2 CO CH4 important for water-poor atmosphere H2O Summary OH and O radicals drive most of chemical reactions H2O plays as a catalyst in producing H H production is insensitive to the exact abundances of H2O, CO, and CH4, 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 0.46 MJ, 0.05 AU, e ~ 0.013, G2 Goukenleuque et al. 2000 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 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 1-D model technical detail mass continuity ni/t + i/z = Pi Li I = -Di[ni/z + ni/Hi + n(1+i)/T T/z] -K[ni/z + ni/Ha + n/T T/z] Hi and Ha 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 <ni/t> 0 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*u2=const) – constant below tropopause – exponential decay above tropopause Timescales Radiative relaxation timescale of the atmosphere (cp/Teff3) – 1 day (~10 days on Earth, ~1000 days on Jupiter) Eddy diffusion transport timescale – greater than 106 sec at the bottom – less than 1000 sec at the top Hydrodynamic loss Escape parameter: esc (GMpm/r)/(kT) 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 Survey of extrasolar planets Debra Fishcer 2003 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 California & Carnegie Planet Search website http://exoplanets.org/ Determination of planet’s orbital and physical properties HD 209548 Mazeh et al. 2000 Charbonneau et al. 2000 amplitude + period Msin i + Torbit duration + obscuration R + i Atmospheric features Sodium line Na D lines detected, ~4 sigma detection (2.320.57)10-4 Charbonneau et al. 2002 Atmospheric features Atomic hydrogen hydrogen in the atmosphere, – 15 4% detection larger than Roche lobe (?), 3.6 RJ -> 10% maximum over exaggerated planet Vidal-Madjar et al. 2003 Results CO2 Production OH + CO CO2 + H CH4 Production CO + h C + O C + H2 + M 3CH2 + M 2 3CH2 C2H2 + 2H C2H2 + H + M C2H3 + M C2H3 + H2 C2H4 + H C2H4 + H + M C2H5 + M C2H5 + H 2CH3 CH3 + H + M CH4 + M source of hydrocarbons H Production high H/H2 ratio H2O + h H + OH OH + H2 H2O + H UV-flux limited H2O Production CO + h C + O O + H2 OH + H OH + H2 H2O + H important for water-poor atmosphere Barman et al. (2002) T-P profiles Fortney et al. (2003) T-P profiles Barman et al. (2002) T-P profiles Fortney et al. (2003) T-P profiles this work cross section (cm-2) wavelength (angstrom)
