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Exoplanet Atmospheres and Interiors Types of Planets

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Exoplanet Atmospheres and Interiors Types of Planets Exoplanet Atmospheres and Interiors Types of Planets • Hot Jupiters – Most common, because of observaonal biases – Temperatures ~ 1000K • Neptunes – May resemble the gas giants in our solar system • Super-earths – Rocky? – Water planets? • Terrestrial Atmosphere Basics • Ρ(h) = P(0) e-h/h0 • h0=kT/mg – k = Boltzmann constant – T=temperature – m=mass of par?cle – g=gravitaonal acceleraon • Density falls off exponen?ally with height Atmospheric Complicaons Stars have relavely simple atmospheres • A few diatomic molecules Brown Dwarfs and Planets are more complex • Temperature Inversions (external heang) • Clouds – Probably exist in T dwarfs – precipitaon • Molecules • Chemistry Generalized Thermal Atmosphere • Blue regions are convecve = lapse rate Marley, ARAA, fig 1 Atmospheric Chemistry • Ionizaon equilibrium • Chemical equilibrium High T Low T Low P High P Marley, ARAA, Fig 4 Marley, ARAA, Fig 3 • 2 MJ planet, T=600K, g=10 Marley, ARAA, Fig 5 Condensaon Sequence Transit Photometry Transit widths may reveal high al?tude haze 2 2 Excess eclipse depth δ ≃ ((Rp+ nH)/R∗) – (Rp/R∗) H = pressure scale height n = number of scale heights For typical hot Jupiters, δ ≅ 0.1% Observaons: Photometry • Precision photometry of transi?ng planet can give temperature – Comparison with Teq gives albedo (for Rp) • Inference of Na D1,D2 lines in HD 209458: – Eclipse 0.0002 deeper in lines – Charbonneau et al 2002, ApJ, 568, 377 Observaons: Photometry • Precision photometry of transi?ng planet can give temperature 2 2 – fin = (1-A) L* πRp / 4πd 2 4 – fout = 4πRp σTp – Comparison with Teq gives albedo (for Rp) For A=0: TP=T*√(R*/2d) Hot Jupiters • A is generally small: no clouds • Phase curve -> atmospheric dynamics • Flux variaons -> day to night temperature variaons • Hot Jupiters expected to have jet streams Basic Atmospheric Circulaon – no rotaon (Hadley cells) Jupiter HD 189733b • Temperature: 970-1200K • Peak 30o East • Winds up to 8700 km/h • H atm. – 5% eclipse – (planet: 2.4%) – m-dot: 1010 g/s • P=2.2 days HD 189733b • Temperature: 970-1200K • Peak 30o East • P=2.2 days • H2 atm. • Blue color – Mie sca. – MgSiO3? Clouds in Kepler 7b • A=0.35 • Brightest point 41o west of substellar point • Minimum 25o east of substellar point • Demory et al. 2013 Observaons: Spectroscopy • Transmission spectroscopy of transi?ng planet NASA release 14-255 Observaons: Spectroscopy • Transmission spectroscopy of transi?ng planet Berta et al. 2012, NASA release 14-255 ApJ, 747, 35 Direct spectroscopy (BDs) • HR 8799c Water in 51 Peg b • Birkby et al. 2017, AJ, 153, 3 Water in 51 Peg b • Atmospheric Evaporaon • Important in hot Jupiters • Due to XUV irradiaon 3 – mass loss ~ επR FXUV/GMpKde • Example: HD 209458b (Vidal-Madjar et al. 2003, Nature, 422, 143) Atmospheric Evaporaon HD 209458b (Vidal-Madjar et al. 2003, Nature, 422, 143) 10 11 • m-dot ~ 10 -10 g/s (0.05 M⊕/Gyr) Planetary Interiors 3 • ρ = mp/(4/3π rp ) -3 • ρ = 1 gm cm : H2O • ρ < 1 gm cm-3: gas giant • ρ > 1 gm cm-3: rocky • Note: densi?es must be adjusted for compressibility Uncompressible: R ~ M-1/3 Gas Giants • H/He composi?on • EoS not well known under Jovian condi?ons – 20,000K, 70 Mbar • Metallic H needed to generate B fields Terrestrial Planets Composi?on: O, Fe, Mg, Si (+Ni, Ca, Al, S) • Core – Solid Fe – Liquid Fe + FeS outer core • Mantle – Inner mantle: • Perovskite (Mg,Fe)SiO3 • Magnesiowüs?te (Mg,Fe)O • Outer Mantle – Olivine (Mg,Fe)2SiO4 – Orthopyroxene (Mg,Fe)2Si2O6 – Clinopyroxene Ca(Mg,Fe)Si2O6 – Garnet (Ca,Mg,Fe,Mn)3 (Al,Mn,Fe,V,Cr)2 (SiO4)3 • Crust Small composi?onal differences do not measurably affect EoS Super-Earths • None available for detailed comparison • Models: R ~ M -0.274 (1 < M/M⊕ < 10) Planetary Surface Temperatures 4 4 4 • Tp = Tint + Teq • At young ages, Tint >> Teq • Tint from – Heat of accre?on – Gravitaonal semling – Radioac?ve decay – Ohmic dissipaon (hot Jupiters) – Tidal heang (non-zero e; binaries) • At the age of the solar system, Tint negligible Compability with Earth Details depends on • Rotaon • Insolaon • H2O abundance • Important for consideraons of habitability ½ ½ 2 1/8 Teq= (R* T*) /((2 a) (1-e ) ) Aside: Rogue Planets SIMP J013656.5+093347 • Spectral type: T2.5 • R sin i: 1.02 ± 0.02 RJup • τ< 950Myr (based on evolu?onary models) • Possible member of Car-near MG – 200 Myr – M: 12.7 ± 1.0 RJup – 0.2% probability of interloper • Gagné et al. 2017, ApJL, 841, L1 SIMP J013656.5+093347 The Coldest Brown Dwarf WISE J085510.83-071442.5 • Teff : 225-260K (Luhman 2014b, ApJL, 786, L18) • M: 1-10 MJup for ages 1-10 Gyr • π: 0.448±0.033 arcsec (Wright et al. 2014, AJ, 148, 82) • µ: 8.08±0.05 “/yr • d=2.23 pc; vtan= 85±9 km/s • Possible H2O clouds (Faherty et al. 2014 ApJL, 793, L16) .
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