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Characterizing exoplanets atmospheres and surfaces Thérèse Encrenaz LESIA, Observatoire de Paris Pathways Toward Habitable Planets Barcelona, 14-18 September.

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Presentation on theme: "Characterizing exoplanets atmospheres and surfaces Thérèse Encrenaz LESIA, Observatoire de Paris Pathways Toward Habitable Planets Barcelona, 14-18 September."— Presentation transcript:

1 Characterizing exoplanets atmospheres and surfaces Thérèse Encrenaz LESIA, Observatoire de Paris Pathways Toward Habitable Planets Barcelona, September 2009

2 Outline The planetary zoo Rocky Exoplanets (warm) –Spectral variations with spectral type, R H, abundances –Atmosphere: constraints on resolving power –Surface: mineralogy, Red Vegetation Edge Icy Exoplanets (cold) –Atmosphere: constraint on R –Surface: ices Giant Exoplanets (from hot to very cold) –Atmosphere: importance of thermal profile, constraint on R Conclusions

3 Spectroscopy of an exoplanet Reflected starlight component (UV, visible, near-IR) –Albedo is about 0.3 for most of solar-system planets –Absorption lines or bands in front of stellar blackbody Thermal component (IR, submm & mm) –Mostly depends upon the temperature of the emitting region –Emission 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, H 2, N 2, radicals) The IR range is best suited for probing exoplanets neutral atmospheres

4 The Solar System: A planetary zoo Planets with an atmosphere Rocky planets (warm) –Mars-type (CO 2, N 2 + H 2 O)No stratosphere –Earth-type (N 2, O 2 + H 2 O)Stratosphere (O 3 ) Icy planets (cold) –Titan-type (N 2, CH 4 + CO)Stratosphere (hydrocarbons, nitriles) Giant planets (cold to very cold) –Jupiter-type (H 2, CH 4, NH 3 +H 2 O)Stratosphere (hydrocarbons) –Neptune-type (H 2, CH 4 )« Bare planets –Mercury/asteroid-type (refractories) –TNO-type (ices)

5 Te (K) Stellar distance (AU) (solar-type star) Small Exoplanet (WARM)(COLD) ( M E ) No atmosphere Atmosphere Atmosphere (Mercury-type) N 2, CO 2, CO, H 2 N 2, CH 4 (+CO) ( Mars-Venus type) hydrocarbons, nitriles if O 2 -> O 3 (Earth-type) (Titan-type) STRATOSPHERE Giant Exoplanet (HOT) (WARM) (COLD) ( M E ) Atmosphere Atmosphere Atmosphere H 2,CO,N 2,H 2 OH 2,CH 4,NH 3,H 2 O H 2,CH 4 hydrocarbons hydrocarbons (Jupiter-type) (Neptune-type) STRATOSPHERE What kind of exoplanet can we expect? [ F*/D 2 ](1-a) = 4 Te 4

6 Te (K) Stellar type A (T=10000 K) F (T=7000 K) G (T=5700 K) K (T=4200 K) M (T=3200 K) HZ Variations of asterocentric distances with the stellar type

7 However, this is not so simple! Why? Other parameters are involved: –Albedo -> effect on Te –Rotation period -> effect on Te Phase-locked planets -> strong day/night contrasts –Possible greenhouse effect -> may increase Ts vs Te Earth: 15 K; Venus: over 200 K –Obliquity Atmospheric dynamics -> may change day/night contrasts –Magnetic field -> may prevent atmospheric escape Migration is possible!

8 Rocky Planets The IR spectrum of Mars (ISO-SWS) Spectral signatures: CO 2, H 2 O, CO (+ traces H 2 O 2, CH 4 ) H2OH2O CO 2 CO CO 2 Lellouch et al., 2000 Hydrated silicates CO 2 Ps = 6 mb

9 Variation of a Mars-type spectrum as a function of the stellar type (D = 1 UA) Stellar Type A (10000 K) F (7000 K) G (5700 K) K (4200 K) Te (K)

10 Variation 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 UA Te = 1000, 863, 496, 273 K NB: For small D, the reflected component dominates -> Atmospheric signatures mostly in absorption

11 Variation with atmospheric composition: H 2 O-dominated (Earth-like) spectrum (above clouds) H 2 O H 2 O CO 2 CO 2 H 2 O ice Pcl = 10 mb

12 The infrared spectrum of the Earth as seen by the NIMS instrument aboard Galileo (Earth flyby, December 1990) Drossart et al., 1993

13 The thermal spectrum of telluric planets Venus Earth Mars Hanel et al., 1992

14 Thermal spectra of rocky planets Resolving power required : CO 2 = 3 m R = 3 O 3 = 1 mR = 10 CH 4 = 0.15 mR = 50 Earth Mars Venus Earth R=70,10,5

15 Hanel et al., 1992 Solid signatures in rocky planets Mid-latitudes Tsurf > Tatm Polar cap Tsurf < Tatm Silicates: cm-1(broad) Water ice: cm-1 (broad) Reflected spectrum: H 2 O ice1.25, 1.5, 2.0 m Silicates1.0, 2.0 m (broad) Ferric oxides1.0 m Carbonates2.35, 2.5 m Hydrated silicates m (broad) Thermal spectrum: H 2 O ice silicates

16 The Red Vegetation Edge (Earth spectrum) Seager et al. 2005

17 RVE : Earthshine observations Seager et al Problems: -partial coverage of the vegetation -clouds (20-30% of the disk)

18 The reflected spectrum of a CH 4 -dominated planet (icy or giant) Larson, 1980

19 The atmosphere of an icy planet: The thermal component Titan - SWS: CH 4, hydrocarbons, nitriles Resolving power required: R > 5 ( C 2 H 2 -C 2 H 6 ) ; R > 10 (CH 4 ) CH 4 C2H6C2H6 HCN, C 2 H 2

20 Solid signatures on icy planets H 2 O ice H 2 O, CH 4, CO, N 2 (Ganymede) (Pluto)

21 The atmosphere of two gaseous giants: The thermal component Jupiter & Saturn - ISO-SWS CH 4 CH 3 D, PH 3 NH 3 C2H6C2H6 Jupiter Saturn NB: Jupiter and Saturn are VERY different! PH 3

22 Jupiter -SWS The m range: CH 4, CH 3 D, C 2 H 6, NH 3, PH 3 Resolving power required: - for NH 3 detection: R > for CH 4 detection: R > 150 -for C 2 H 6 detection: R > 20

23 The atmosphere of an icy giant Neptune - SWS The range: CH 4, CH 3 D, C 2 H 2, C 2 H 6 Resolving power required: R > 5 ( C 2 H 2 -C 2 H 6 ) ; R > 10 (CH 4 ) CH 4 C 2 H 6 C 2 H 2

24 In summary… The diversity in solar-system bodies opens the same possibilities for exoplanets A resolving power higher than 10 is required for the identification of major gaseous and solid signatures In the thermal range, hydrocarbons (C 2 H 2, C 2 H 6 ) are easier to detect than methane Knowing the thermal structure is essential for interpreting thermal spectra No stratosphere expected for Rocky Exoplanets (N 2, CO 2, H 2 O) except if O 2 is present A stratosphere is expected for Icy Exoplanets (N 2, CH 4 ) and Giant Exoplanets (H 2, CH 4,…)


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