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The Upper Atmospheres of Extrasolar Gas Giants in 3D

The Upper Atmospheres of Extrasolar Gas Giants in 3D. T.T.Koskinen, A.D.Aylward, S.Miller Centre for Planetary Sciences Department of Physics and Astronomy, University College London Molecules 2008, Paris, France. Transit of HD17156b (Antonio Cagnoli). EXOTIM output. Hydrostatic equilibrium.

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The Upper Atmospheres of Extrasolar Gas Giants in 3D

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  1. The Upper Atmospheres of Extrasolar Gas Giants in 3D T.T.Koskinen, A.D.Aylward, S.Miller Centre for Planetary Sciences Department of Physics and Astronomy, University College London Molecules 2008, Paris, France Transit of HD17156b (Antonio Cagnoli) EXOTIM output

  2. Hydrostatic equilibrium Viscosity (due to molecular diffusion) EXOTIM 3D equations of motion in spherical pressure coordinates (Eulerian co-rotating frame) Continuity Pressure range: 2 mbar - 3.7 pbar Momentum Energy equation Equations return r, u and T at every point in the 3D grid.

  3. Reaction rates

  4. Exobase: ncHcs ≈ 1 Jeans escape flux Thermal escape parameter Limiting flux Evaporation Escape velocity Jupiter: vesc 60 kms-1 Jupiter lc ~ 480

  5. Orbital Distance and Temperature Exobase and effective temperatures vs. orbital distance for a Jupiter-like EGP orbiting a Sun-like star H3+ cooling efficiency and low-pressure (0.008 nbar) mixing ratio of H2 averaged over the dayside Koskinen et al., ApJ, 661, 515-526 (2007)

  6. At 0.2 AU Temperatures and circulation at the upper boundary of the model at 0.2 AU. The maximum winds reach ~2 km s-1. Energy equation terms at the substellar point of the model at 0.2 AU Mixing ratio of atomic hydrogen near the upper boundary of the model as a function of longitude along the equator Substellar electron densities

  7. Hydrostatic ‘Stability’ Limit Fig. 2, Koskinen et al., Nature, 450, 845-848 (2007)

  8. Mass Loss Escape flux (sr-1s-1): (Watson, 1981) Koskinen, T.T, et al., Nature, 450, 845-848 (2007) With parameters appropriate for HD209458b (onset of hydrodynamic escape cooling efficiency ~60 %) 0.045 AU: dM/dt ~ 1.7 x 1010 gs-1

  9. HD17156b Discovered by the N2K consortium (Fischer et al. 2007), transit first detected by amateur astronomers (Barbieri, M. et al., A&A, 476, L13-L16, 2007) The Star Fischer, D.A. et al., ApJ, 669, 1336-1344 (2007): G0 Dist ≈ 78.24 pc , MV ≈ 3.7 Age ≈ 5.7 Gyr , Teff ≈ 6079 K M* ≈ 1.2 MSun , R* ≈ 1.47 RSun Fe/H ≈ 0.24 , Prot ≈ 12.8 days The Planet1,2 Mp ≈ 3.1 MJ , Rp ≈ 1.0 - 1.23 RJ p≈ 1.66 - 3.8 J a ≈ 0.16 AU , P ≈ 21.2 days e ≈ 0.67 , i ≈ 85o - 86.5o 1Gillon, M. et al., A&A, 485, 871-875 (2008) 2Irwin, J. et al., ApJ, 681, 636-643 (2008)

  10. The Orbit  Earth Pseudo-synchronousspin Kepler’s equation for the mean anomaly True anomaly E = Eccentric anomaly HD17156b:  ≈ 121o The orbital distance varies between 0.052 and 0.27 AU. One quarter orbit is reached at -153 degrees. sp ≈ 5.6 <>orbit

  11. EXOTIM globally averaged temperature at p = 0.04 nbar vs. orbital true anomaly 72-91 % cooling function (Exo-1) 0.01-0.24 % cooling function (Exo-2) Mixing ratio of atomic hydrogen determines the cooling efficiency. The plot shows apastron mixing ratios for two different lower boundary values, 2 x 10-4 (solid line) and 0.01 (dotted line). Average Temperatures vesc ~ 108 km s-1 Koskinen et al., ApJ, accepted

  12. Substellar density profiles of the dominant neutral species Substellar electron density profiles at apastron (solid line) and at periastron (dotted line) Exo-1 Above: Substellar P-T profiles at apastron (solid), 1/4 orbit (dotted), periastron (dashed), and 3/4 orbit (dash-dotted) Substellar ion density profiles: H+ (dotted), H3+ (solid), H2+ (dashed), He+ (dash-dotted)

  13. Substellar electron density profiles at apastron (solid line) and at periastron (dotted line) Substellar density profiles of the dominant neutral species Above: Substellar P-T profiles at apastron (solid), 1/4 orbit (dotted), periastron (dashed), and 3/4 orbit (dash-dotted) Substellar ion densities Exo-2 Insert 3D sphere plot

  14. Exobase characteristics (periastron) Exo-1: zc 1.03 Rp lc (H)  200 Hc  180 km Exo-2: zc 1.55 Rp lc (H)  15 Hc  5000 km Evaporation Evaporation of H at periastron (Exo-2) wJ 0.45 cm s-1, dMJ  104 gs-1 [wL  1.9 cm s-1] Mass loss from the Exo-2 simulation based on thermal Jeans escape

  15. Hydrogen Cloud Altitude of the 0.04 nbar pressure level in Exo-1 (solid) and Exo-2 (dotted)

  16. Total H3+ infrared emissions from HD17156b vs. orbital true anomaly H3+ emissions Line fluxes at periastron Total emitted power: 8.6 x 1015 W [~1.17 x 10-22 Wm-2]

  17. Conclusions • We have developed a TGCM for extrasolar giant planets, including an ionosphere in photochemical equilibrium • The nature of the upper atmosphere depends on the composition and the details of the photochemistry, especially on the mixing ratio of H2 • We have applied the model to HD17156b, and find that the atmosphere of this planet is not likely to undergo such fast hydrodynamic escape as has been postulated for close-in giants like HD209458b • Observations of the upper atmosphere can constrain the properties of the lower atmosphere, stellar XUV activity and stellar wind conditions in the vicinity of planets

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