Molecular spectroscopy for planetary and exoplanetary radiative transfer : The rock of Sisyphus or the barrel of the Danaids?

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1 Molecular spectroscopy for planetary and exoplanetary radiative transfer : The rock of Sisyphus or the barrel of the Danaids? Pierre Drossart LESIA, Observatoire de Meudon

2 Situation of molecular spectroscopy for planetary atmospheres Giant planets main IR absorbers : CH 4, NH 3 minor absorbers : PH 3, CO, H2O, etc. Titan main IR absorber : CH 4 Telluric Planets (Venus, Earth, Mars) main IR absorber : CO 2 minor absorbers : H 2 O, CO, etc. 30/08/ th ASA/12th HITRAN Conference - REIMS 2

3 RT in the infrared : vibration-rotation of Vibration rotation bands of CO 2 in the infrared molecules : 1) CO 2 Lopez-Puertas & Taylor, /08/ th ASA/12th HITRAN Conference - REIMS 3

4 vibration/rotation bands: 2) CH µm 3.3 µm 2.3 µm 1.8 µm Dyad 2 vibrational states 2 sublevels Pentad 5 vibrational states 9 sublevels Octad 8 vibrational states 20 sublevels Tetradecad 14 vibrational states 60 sublevels Wenger and Champion, JQSRT, /08/ th ASA/12th HITRAN Conference - REIMS 4

5 Earth transmittance Neglecting scattering e ν = k ν =>No angular dependence in the extinction coefficient (nor in the source function) All the complexity is in the absorption coefficients = molecular spectroscopy CO CH 4 N 2 O CO 2 H 2 O O 3 Lopez-Puertas & Taylor, 2001 all 30/08/ th ASA/12th HITRAN Conference - REIMS 5

6 Radiative transfer non-lte scheme Non-LTE regime: Jν Bν Thermal collision time > radiative time Collisional, chemical processes to be taken into account to calculate the source function Lopez-Puertas & Taylor, /08/ th ASA/12th HITRAN Conference - REIMS 6

7 Non-thermal processes 1. Vibrational-vibrational energy transfer. Example : CO 2 molecule ; exchange with N 2 2. Electronic to vibrational energy transfer. Example: O( 1 D) state excitating the N 2 vibrational modes 3. Chemical recombination or chemiluminescence Example: ozone bands at 10 µm 4. Photochemical reactions Example : O 2 emissions at 1.27 µm 5. Dissociative recombination (O e- O* + O) 6. Collisions with charged particles (auroral processes) 30/08/ th ASA/12th HITRAN Conference - REIMS 7

8 Telluric planets Near infrared spectra Non-LTE effects 30/08/ th ASA/12th HITRAN Conference - REIMS 8

9 The infrared spectrum of Martian atmosphere Solar reflected Thermal CO 2 H 2 O Hydrated CO 2 silicates CO 2 CO CO 2 Reflected sunlight -> mineralogy Thermal emission -> T(z), winds ISO-SWS Lellouch et al., /08/ th ASA/12th HITRAN Conference - REIMS 9

10 Venus nightside windows 2.3 µm CFHT/FTS observations (Res = 0.15 cm -1 ) [Taylor et al. 1997] Altitude range: km Absorbers: CO 2, H 2 O, HDO, CO, OCS, SO 2, HF CO 2 30/08/ th ASA/12th HITRAN Conference - REIMS 10

11 Venus night side spectra Venus Express / VIRTIS Obs. 30/08/ th ASA/12th HITRAN Conference - REIMS 11

12 Comparative planetology: atmosphere of the terrestrial planets Gabriella Gilli, IAA, PhD Thesis 2012 SIMILARITIES UV, soft X-rays absorption in the Thermosphere IR absorption in the mesosphere DIFFERENCES Venus and Mars thermosphere colder than on the Earth O, CO about 10 times more abundant on Venus and Mars Stronger cooling in the upper regions of Mars and Venus by the CO 2 15-µm vibrational excited levels CO 2 vmr on the Earth is 1000 time smaller 1. Limb data from VIRTIS/Vex, PFS/Mex (Formisano et al. 2005) and results from MIPAS/Envisat (Funke et al. 2007) were used. 2. Non-LTE models for Venus (Roldan et al. 2000, López-Valverde et al. 2007), for Mars (Lopez- Puertas and Lopez Valverde 1994) and for the Earth (Lopez-Puertas et al. 2005) 11th ASA/12th HITRAN Conference - REIMS 30/08/

13 Basics on non-lte models for Venus, Mars and the Earth CO µm levels scheme FB band: Transition from 001 level to the ground FH, SH bands: arises from higher energy states CO 2 high energy states directly excited during daytime by solar absorption. Gabriella Gilli, IAA, PhD Thesis th ASA/12th HITRAN Conference - REIMS 30/08/

14 Results from CO µm analysis Altitude variations Similar behaviour in the three planets Variation of the shape of the emission Maximum of the emission at 50 km, 110 km, 100 km on Earth, Venus and Mars. - SH bands - pressure level 1000 times denser on the Earth Gabriella Gilli, IAA, PhD Thesis /08/2012 Lopez-Valverde, Gilli, PSS, th ASA/12th HITRAN Conference - REIMS 14

15 VIRTIS observations for CO 2 non-lte Gilli et al, JGR /08/ th ASA/12th HITRAN Conference - REIMS 15

16 Basics on non-lte models for Venus, Mars and the Earth CO 4.7 µm levels scheme CO 4.7 µm Vibrational temperatures Gilli et al FB and FH bands: main bands responsible for the 4.7 µm emission LTE breakdown for CO(2) occurs at higher pressure then CO(1) in the 3 planets Gabriella Gilli, IAA, PhD Thesis th ASA/12th HITRAN Conference - REIMS 30/08/

17 VIRTIS-H 4.7 µm individual spectra - Individual spectra observed up to 120 km -FH and FB rotational lines identified - FH dominates the CO spectra in the lower mesosphere - VIRTIS-H promising to derive atmospheric parameters Gabriella Gilli, IAA, PhD Thesis /08/ th ASA/12th HITRAN Conference - REIMS 17

18 OH and O 2 emission on Venus A.V. Shakun, PhD Thesis /08/ th ASA/12th HITRAN Conference - REIMS 18

19 Titan Cassini/VIMS Titan T0 CM_ cub (#18) Spectrum in central regions 30/08/ th ASA/12th HITRAN Conference - REIMS 19

20 VIMS DISR comparison 30/08/ th ASA/12th HITRAN Conference - REIMS 20

21 Jupiter & Saturn Near IR spectra Non-LTE CH 4 spectra 30/08/ th ASA/12th HITRAN Conference - REIMS 21

22 Water at 5 µm as seen by NIMS-Galileo Roos-Serote et al, 1999 Map of an IR hot spot on Jupiter (Galileo Visible camera) 5-µm thermal emission (Galileo/NIMS) Variations of water vapor within the hot spot 30/08/ th ASA/12th HITRAN Conference - REIMS 22

23 Simplified scheme of fluorescence in CH 4 in Jupiter grouping stretching/ bending levels of CH 4 CH 4 radiative transitions: ν 3 (3.3µm) ν 4 (7.8µm) 30/08/ th ASA/12th HITRAN Conference - REIMS 23

24 CH 4 fluorescence in Jupiter atmosphere with ISO/SWS Objective with JIRAM: Mapping of the homopause level and CH 4 distribution above the homopause 30/08/ th ASA/12th HITRAN Conference - REIMS 24

25 Cassini/VIMS CH 4 emissions at 3.3 µm Jupiter (2000) Saturn (2005) 30/08/ th ASA/12th HITRAN Conference - REIMS 25

26 Cassini/VIMS Titan observations : resolution 130 km /phase angle 90 Circle = surface of Titan Profiles taken along the segments Limb profiles Peak emission at ~400km 30/08/ th ASA/12th HITRAN Conference - REIMS 26

27 Model (left) and Observed VIMS/T0 rebinned spectra (right) across Titan limb Altitude of the limb spectra raise from blue (1000km) to red (100 km). Shift of the peak from 3.31 to 3.33 at low altitudes <=> fundamental at high altitude / overtone at low altitude 30/08/ th ASA/12th HITRAN Conference - REIMS 27

28 Exoplanets See G. Tinetti presentation Molecules of interest : CH 4, CO 2, H 2 O, CO, etc. Main difference with planetary atmospheres : hot temperatures => many hot bands 30/08/ th ASA/12th HITRAN Conference - REIMS 28

29 Needs for atmospheric modeling Spectroscopy at short wavelengths for major constituents : CO 2, CH 4 Hot temperatures => hot band spectroscopy for exoplanets Minor constituents : H 2 O 2, OH, H 2 CO for telluric planets NH 3, PH 3, H 2 S for giant planets Hydrocarbons and nitriles for Titan Line broadening (H 2 for giant planets) Coefficients for relaxation line mixing Collision induced absorption 30/08/ th ASA/12th HITRAN Conference - REIMS 29