The atmosphere of an extrasolar gas giant planet is a complex system, very often close-in to the parent star, resulting processes that are much more extreme




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НазваниеThe atmosphere of an extrasolar gas giant planet is a complex system, very often close-in to the parent star, resulting processes that are much more extreme
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Summary of Proposal:


The atmosphere of an extrasolar gas giant planet is a complex system, very often close-in to the parent star, resulting processes that are much more extreme than presently observed in our own solar system. Modeling the current state and evolution of such extrasolar planets is thus one of the key goals that need to be accomplished before it is possible to have an understanding of the way in these systems work. The same understanding is needed to properly validate all models coupled with hydrodynamic escape techniques to be utilized in the Virtual Planetary Laboratory (VPL). It is with these broad long term goals in mind that we propose the work described here: to look at the structure, composition, and evolution of extrasolar gas giant planets.


The work we propose is multifaceted and interdisciplinary, including: (1) dynamical and radiative parameterizations; (2) modeling of cloud processes; (3) photochemical and thermochemical modeling; and, (4) modeling of the evaporative escape, diffusion-limited evaporative escape, and hydrodynamic escape in the planetary environment.


Observations have been recently made of extrasolar hot “Jupiter-type” planets and a unique opportunity to compare modeling results with observations presents itself for the first time in the form of this proposal. Answers to the questions posed in this study are important not only for extrasolar gas giants, but also for understanding the past history of the Earth and for other planets in our solar system and extrasolar terrestrial planets that underwent hydrodynamic escape processes. Recent progress in modeling of planetary atmospheres suggests that an essentially correct understanding of the atmospheric radiative and chemical environment can be attained. The proposed research is a first step in answering these questions by focusing on the problem of extrasolar hot gas giants.


Scientific/Technical/Management Section:


In this work we propose an innovative synergistic study of the interactions that occur in the atmospheres of extrasolar gas giant planets. A program is proposed that will allow the characterization and theoretical understanding of these planets via comparison of modeling with observations. Emphasis will be on the structure, composition and evolution of “close-in” hot Jovian type planets. Initially we shall treat these components separately, but the resultant analysis will be used to couple photochemical, hydrodynamic escape, and radiative equilibrium models to address the following kinds of issues: (1) What is the cloud structure in the atmosphere of such planets; (2) What is the distribution of species of hot “close-in” extrasolar gas giants compared to relatively colder gas giants in our own solar system or known brown dwarfs; (3) What are the sources of atomic hydrogen in the atmosphere; (4) Is the D/H ratio of these planets comparable to the ISM; (5) How stable is this atmosphere when considering hydrodynamic escape of species; and (6) Does this lead to hydrogen depleted “Neptunes”.

The photodissociation of CH4 and the subsequent reactions of the constituents with hydrogen produce all the other hydrocarbons present in a Jovian-type atmosphere (Strobel, 1973). For low temperature and solar insolation, the main source of H is from H2 and CH4 photodissociation and the main sink via C2H2, which we regard as a sufficient catalyst in recombining H. We argue that the chemistry is relatively straightforward for modeling the composition of the atmosphere as higher order hydrocarbon species are readily photylised in the atmosphere of hot extrasolar gas giant planets. Hence, the model can be based on the four main constituents H2, CO, H2O, and CH4. For gas giants very close to their parent star the formation of hydrocarbons, oxygen chemistry, and hydrodynamical loss are significantly enhanced due to high solar insolation and low surface gravity. The details are discussed in M. Liang et al., 2003 and we will use this model as the basis for the chemical model (cf. Figures 1 and 2).



The dynamical and radiative parameterizations include convection, conduction, and effective vertical eddy diffusion rates (H. Savijarvi, 1995; 1999). Parallel development of cloud processes will be done and will include condensation, evaporation of particles, effects on their size distribution, rainout rates, and atmospheric volatile mass budget (Akerman and Marley, 2001; Imamura and Hashimoto, 2001). Each of these modules will be developed and tested as independent subroutines with very simple driver programs.   They will initially be knitted together in the simplest way, viz., we might use an existing radiative equilibrium code to calculate 'constant' radiative heating and cooling that are then used in the convection model to test its stability and its time evolution as it approaches convergence.  The resulting vertical eddy diffusion profile could then be adopted as a constant value and used to test these properties

in the cloud model. Once the the behavior of the convective and cloud/volatile model components are understood, we will re-integrate them with the radiative components into a new thermal equilibrium model applicable to this problem.


We will treat evaporative escape, diffusion-limited evaporative escape, and hydrodynamic escape, dependent upon the physical conditions of the planetary atmosphere and incident external heating. A new technique will be developed for the treatment of hydrodynamic loss (Parkinson et al., 2003a). Although planetary wind models have been created in the past (Watson et al., 1981; Kasting and Pollack, 1983; Chassefiere, 1996) the numerical methods employed to date have not been sufficiently robust to permit the modeling of detailed physics, and to simultaneously allow the exploration of a wide variety of different atmosphere types. These authors solved the hydrodynamic escape problem by integrating the coupled, time independent mass, momentum, and energy equations for the escaping gas from the homopause out to infinity. One of the main difficulties utilizing this method of solution is the existence of a singularity (critical point) in the one-dimensional, steady state solution at the distance where the outflow becomes supersonic. Generated solutions are then either ill-conditioned or provide solutions for a limited subset of cases. However, stable numerical methods exist for the solution of such problems that allow for the generalized treatment of hydrodynamic escape. The Godunov method (Godunov, 1959) has been successfully implemented to study one-dimensional cometary winds (Gombosi et al., 1985) and will be the technique we use for this study. This method overcomes the instabilities inherent in modeling transonic conditions by solving the coupled, time dependent mass, momentum, and energy equations. A detailed description is given of a first order Godunov scheme by Gombosi (1984) and Leveque (2002).


The impact of the proposed research will greatly enhance our understanding of gas giant planets by allowing us to make a direct comparison of the modeling with observations. Numerous searches for an atmospheric signature in the IR-optical wavelength range failed (Bundy and Marcy, 2000; Rauer et al., 2000; Moutou et al., 2001) until the detection with HST of the dense lower atmosphere of HD209458b (recently dubbed Osiris (A. Vidal-Madjar, private communication) observed through the Na I neutral sodium absorption (Charbonneau et al., 2002).

Recent HST observations in the UV of the extended upper atmosphere of an extra-solar planet have been made (Vidal-Madjar et al. 2003). They detected the H I atomic hydrogen absorption

over the stellar Lyman-alpha line during three transits of Osiris. An absorption of 15+/-4% was observed. A comparison with models showed that this absorption should take place beyond the

Roche limit and could thus be understood in terms of escaping hydrogen atoms. Our proposed research could facilitate modeling this condition for Osiris allowing for the first time a way to validate hydrodynamic escape for planetary objects. In the future, this generalized technique could be applied to new extrasolar close-in gas giant planetary observations as data becomes available as well as for hydrogen escape from terrestrial planets (Liu and Donahue, 1976; Hunten and Strobel, 1976, Nair et al., 1994) in the VPL (Parkinson et al., 2003b)


References:


Ackerman, A.S., and Marley, M.S., 2001. Precipitating Condensation Clouds in Substellar Atmospheres, Astrophys. J., 556, 872—884.

Chassefiere, E., 1996. Hydrodynamic escape of hydrogen from a hot water-rich atmosphere: The case of Venus, J. Geophys. Res., 101, 26,039—26,056.

Godunov, S.K., 1959. A difference method for numerical calculation of discontinuous solutions of the equations of hydrodynamics, Mat. Sb., 47, 271—306.

Gombosi, T.I., Cravens, T.E., and Nagy, A.F., 1985. Time Dependent dusty gasdynamical flow near cometary nuclei, Ap. J., 293, 328—341.

Hunten, D.M. and D.F. Strobel, 1974. J. Atmos. Sci., 31, 305-317.

Kasting, J., and Pollack, J.B., 1983. Loss of water from Venus I. Hydrodynamic Escape of hydrogen, Icarus, 53, 479--508.

Imamura, T., and Hashimoto, G.L., 2001. Microphysics of Venusian Clouds in Rising Tropical Air, Amer. Meteorol. Soc., 58, 3597—3612.

Leveque, R.J., 2002. Finite volume methods for hyperbolic problems, Cambridge University Press.

Liang, M-C., Lee, A.Y.T., Yung, Y.L., Parkinson, C.D., and Seager, S., 2003. Source of Atomic Hydrogen in the Atmosphere of HD209458b, Paper in Preparation.

Liu, S.C. and T.M. Donahue, 1974.J. Atmos. Sci., 31, 1466-1470.

Nair, H., et al, 1994. Icarus, 111, 124-150.

Parkinson, C.D., Richardson, M.I., and McConnell, J.C., 2003a. Time Dependent Hydrodynamic Flow in Planetary Atmospheres, Paper in Preparation.

Parkinson, C.D., et al., 2003b. Astronomical Detection of Biosignatures from Extrasolar Planets: Virtual Planetary Laboratory (VPL) Architecture and Model Validation, Proc. AAS Bull.

Savijarvi, H., 1999. A model study of the atmospheric boundary layer in the Mars Pathfinder lander, Q. J. R. Meteorol. Soc., 125, 483—493.

Savijarvi, H., 1995. Mars Boundary layer Modeling: Diurnal Moisture Cycle and Soil Properties at the Viking Lander 1 Site, Icarus, 117, 120—127.

Yung, Y.L. and W.B. DeMore, 1998, Photochemistry of Planetary Atomspheres. NY: Oxford University Press.


Biographical Sketch – Christopher D. Parkinson

PERSONAL: Address: Work – Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109

Phones: Work: 818-393-7596

Social Security #: 606-35-6678;

Citizen of Canada: email: chris.parkinson@.jpl.nasa.gov



Selected Publications


J.C. McConnell, C. D. Parkinson, L. Ben Jaffel, C. Emerich, R. Prangé, and A. Vidal-Madjar, 1989, H Lyman--alpha emission at Neptune: Voyager Prediction, Astron. Astrophys., 225, L9—L12.

C.D. Parkinson, J.C. McConnell, B.R. Sandel, R.V. Yelle, and A.L. Broadfoot, 1990, He 584 Å Dayglow at Neptune, Geophys Res. Lett.,17, 1709—1712.

R.J. Vervack, B. R. Sandel, G.R. Gladstone, J.C. McConnell, and C.D. Parkinson, 1995, Jupiter’s He 584 Å Dayglow: New results, Icarus, 114, 163—173.

C.D. Parkinson, E. Griffioen, J.C. McConnell, G.R. Gladstone, and B.R. Sandel, 1998, He 584 Å Dayglow at Saturn: A Re-assessment, Icarus, 133, 210—220.

C.D. Parkinson, E. Griffioen, J.C. McConnell, L. Ben-Jaffel, A. Vidal-Madjar, J.T. Clarke, and G.R. Gladstone, 1999, Estimates of Atomic Deuterium Abundance and Lyman-alpha Airglow in the Thermosphere of Jupiter, Geophys. Res. Lett., 26, 3177—3180.

C.D. Parkinson, J.C. McConnell, and L. Ben-Jaffel, 2001, Deuterated Ethane in the Jovian Thermosphere, Paper in Preparation.


C.D. Parkinson, L. Ben-Jaffel, and J.C. McConnell, 2001, Determination of the D/H Ratio in the Jovian Atmosphere, Planet. Space Sci. (special Issue).

C.D. Parkinson, J.C. McConnell, R. Prangé, and T. Fouchet, H2O and CO Distribution with Hydrocarbon Photochemistry in the atmosphere of Saturn, Paper in Preparation.

R. Prangé, L. Pallier, J.E.C. Connerney, R. Courtin, J.C. McConnell, and C. D. Parkinson, Dynamical changes in the FUV aurora of Saturn, Paper in preparation.

W.E. Ward, W.A. Gault, G.G. Shepherd, I.C. McDade, M. Kowalski, D.Y. Wang, J.C. McConnell, D. Michelangeli, C. D. Parkinson, J. Caldwell, N. Rowlands and S. Wang, S. Bougher, and J. Fox, Design possibilities for a field-widened Michelson interferometer for wind and temperature measurements in planetary atmospheres, Paper in preparation.

C.D. Parkinson, L. Ben-Jaffel, and J.C. McConnell, Submitted 2003, Deuterium Abundance from HD and CH3D Reservoirs in the Atmosphere of Jupiter, J. Geophys. Res. (Planets).

C.D. Parkinson, J.C. McConnell, E. Griffioen, and L. Ben-Jaffel, Submitted 2003, Deuterium Chemistry and Emission in the Jovian Thermosphere, Icarus.

Liang, M-C., Lee, A.Y.T., Yung, Y.L., Parkinson, C.D., and Seager, S., 2003. Source of Atomic Hydrogen in the Atmosphere of HD209458b, Paper in Preparation.


Parkinson, C.D., Richardson, M.I., and McConnell, J.C., 2003. Time Dependent Hydrodynamic Flow in Planetary Atmospheres, Paper in Preparation.

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