Presentation on theme: "Characterizing exoplanets’ atmospheres and surfaces"— Presentation transcript:
1Characterizing exoplanets’ atmospheres and surfaces Thérèse EncrenazLESIA, Observatoire de ParisPathways Toward Habitable PlanetsBarcelona, September 2009
2Outline The planetary zoo Rocky Exoplanets (warm) Spectral variations with spectral type, RH, abundancesAtmosphere: constraints on resolving powerSurface: mineralogy, Red Vegetation EdgeIcy Exoplanets (cold)Atmosphere: constraint on RSurface: icesGiant Exoplanets (from hot to very cold)Atmosphere: importance of thermal profile, constraint on RConclusions
3Spectroscopy of an exoplanet Reflected starlight component (UV, visible, near-IR)Albedo is about 0.3 for most of solar-system planetsAbsorption lines or bands in front of stellar blackbodyThermal component (IR, submm & mm)Mostly depends upon the temperature of the emitting regionEmission lines in the stratosphere, absorption lines in the troposphere (function of T(P))Fluorescence emission (UV, visible, near-IR)Emission lines in the upper atmospheres (H, H2, N2, radicals)The IR range is best suited for probing exoplanets’ neutral atmospheres
4The Solar System: A planetary zoo Planets with an atmosphereRocky planets (warm)Mars-type (CO2, N2 + H2O) No stratosphereEarth-type (N2, O2 + H2O) Stratosphere (O3) Icy planets (cold)Titan-type (N2, CH4 + CO) Stratosphere (hydrocarbons, nitriles)Giant planets (cold to very cold)Jupiter-type (H2, CH4, NH3 +H2O) Stratosphere (hydrocarbons)Neptune-type (H2, CH4) « Bare planetsMercury/asteroid-type (refractories)TNO-type (ices)
6Variations of asterocentric distances with the stellar type Te (K)Stellar typeA(T=10000 K)F(T=7000 K)G(T=5700 K)K(T=4200 K)M(T=3200 K)HZ
7However, this is not so simple! Why? Other parameters are involved:Albedo -> effect on TeRotation period -> effect on TePhase-locked planets -> strong day/night contrastsPossible greenhouse effect -> may increase Ts vs TeEarth: 15 K; Venus: over 200 KObliquityAtmospheric dynamics -> may change day/night contrastsMagnetic field -> may prevent atmospheric escapeMigration is possible!
8Rocky Planets The IR spectrum of Mars (ISO-SWS) Ps = 6 mb CO2CO2H2OCOHydratedsilicatesCO2CO2Spectral signatures: CO2, H2O, CO (+ traces H2O2, CH4)Lellouch et al., 2000
9Variation of a Mars-type spectrum as a function of the stellar type (D = 1 UA)Te (K)476346273174StellarTypeA(10000 K)F(7000 K)G(5700 K)K(4200 K)
10Variation of a Mars-type spectrum as a function of the asterocentric distance D(solar-type star)D = 0.07, 0.1, 0.3, 1.0 UATe = 1000, 863, 496, 273 KNB: For small D, the reflected component dominates-> Atmospheric signatures mostly in absorption
21The atmosphere of two gaseous giants: The thermal component Jupiter & Saturn - ISO-SWSJupiterSaturnCH3D, PH NH3C2H6PH3CH4NB: Jupiter and Saturn are VERY different!
22Jupiter -SWS The 6-12-mm range: CH4, CH3D, C2H6, NH3, PH3 Resolving power required:- for NH3 detection: R > 100- for CH4 detection: R > 150-for C2H6 detection: R > 20
23The atmosphere of an icy giant Neptune - SWS The 2-18-m range: CH4, CH3D, C2H2, C2H6CH C2H C2H2Resolving power required: R > 5 ( C2H2-C2H6) ; R > 10 (CH4)
24In summary…The diversity in solar-system bodies opens the same possibilities for exoplanetsA resolving power higher than 10 is required for the identification of major gaseous and solid signaturesIn the thermal range, hydrocarbons (C2H2, C2H6) are easier to detect than methaneKnowing the thermal structure is essential for interpreting thermal spectraNo stratosphere expected for Rocky Exoplanets (N2, CO2, H2O) except if O2 is presentA stratosphere is expected for Icy Exoplanets (N2, CH4) and Giant Exoplanets (H2, CH4,…)