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Spectroscopy of Titan's upper atmosphere with the Ultraviolet Imaging Spectrograph in Cassini

Spectroscopy of Titan's upper atmosphere with the Ultraviolet Imaging Spectrograph in Cassini. Fernando J. Capalbo*, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Et-touhami Es-sebbar, Tommi T. Koskinen, Roger V. Yelle, Bill R. Sandel, Gregory M. Holsclaw, William E. McClintock

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Spectroscopy of Titan's upper atmosphere with the Ultraviolet Imaging Spectrograph in Cassini

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  1. Spectroscopy of Titan's upper atmosphere with the Ultraviolet Imaging Spectrograph in Cassini Fernando J. Capalbo*, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Et-touhami Es-sebbar, Tommi T. Koskinen, Roger V. Yelle, Bill R. Sandel, Gregory M. Holsclaw, William E. McClintock *fernando.capalbo@lisa.u-pec.fr PROGRAMME NATIONAL DE PLANETOLOGIE (PNP) Quadrennial Seminar October 2014 Paris, France

  2. Titan’s atmosphere Titan from UVIS

  3. Introduction – Titan’s atmosphere From: Ed Brown et al., Titan from Cassini Huygens, Thermosphere AER further chemical evolution? Credits: NASA Temporal and horizontal variability Magee et al., 2009 Wodarg et al., 2008 Titan from UVIS

  4. Introduction – Motivations and focus Koskinen et al., 2011. UVIS Stellar occultations: _ Analyzed: scarce _ N2 only recently (Kammer et al., 2013) Solar occultations: _ This work 500 – 1000 km Main contributions: _ C6H6 acs _ N2, CH4 and other profiles. Temperature vs. position, time.. _ Temperature variability. Titan from UVIS

  5. UVIS instrument and observations Titan from UVIS

  6. UVIS stellar and solar occultations Titan from UVIS

  7. Benzene absorption cross sections Titan from UVIS

  8. Benzene ACS in the VUV - Introduction In Titan Experiments (Imanaka 2010) Models (Lebonnois,2005) Measurements (Koskinen, 2011) 10-6 (Vinatier et al., 2010) Mechanisms of formation? vertical distribution?  UVIS Benzene ACS ACS Highly explored. No temperature studies. Titan from UVIS

  9. Benzene ACS in the VUV - Measurements Synchrotron radiation, BESSY II facility, Berlin. Titan from UVIS

  10. Benzene ACS in the VUV - Measurements Pressure gauge Temperature sensor 10 m long vacuum chamber Interchangeable slit Diffraction grating Absorption Cell C6H6 Deuterium lamp UV radiation Image processing Photosensitive screens Cooling system Optical Scanner Images of Absorption spectrum Manual transfer After exposure 100 Å Deuterium lamp radiation, Meudon Observatory facility, Meudon. Analysis process Titan from UVIS

  11. Benzene ACS in the VUV – Results, temperature variation analysis No significant temperature variations. Titan from UVIS

  12. UVIS stellar occultations: minor constituents Titan from UVIS

  13. Abundance of minor constituents (FUV stellar occultations) – Hydrocarbons, nitriles. T41 Solid profiles from Koskinen et all., 2011. T53 Titan from UVIS

  14. Abundance of minor constituents (FUV stellar occultations) – Aerosols, C6H6 AER horizontal/temporal distribution combining occultations T41: 5 S, Feb 2008 T53: 40 N, Apr 2009 Solid lines: Koskinen et all., 2011. Titan from UVIS

  15. UVIS solar occultations: N2 and CH4 Titan from UVIS

  16. Abundance of mayor constituents (FUV stellar EUV solar occultations) N2 CH4 Titan from UVIS

  17. Abundance of mayor constituents (FUV stellar EUV solar occultations) UVIS FUV – EUV synergy T53 25 S 40 N Titan from UVIS

  18. Temperature and variability Titan from UVIS

  19. Temperature and variability – Some and all flybys Temperatures: global averaged and for particular flybys Horizontal variability: latitudinal and longitudinal Temporal variability: seasonal, solar cycle, diurnal, magnetospheric, and secular effects. T vs. Lat Titan from UVIS

  20. Summary _ C6H6 ACS vs. T _ 2 stellar occ.  profiles of minor species (CH4, C6H6) _ 8 solar occ.  CH4, N2, T _ T variability (new locations/times) Further work _ Analyze more stellar occ.  further analysis of C6H6 and AER profiles _ Cassini Solstice mission 2017  Solar driven variability? _ Coupling data with low atmosphere (CIRS) Titan from UVIS

  21. That’s all, thank you.

  22. BACKUP SLIDES

  23. Introduction – Why Titan? Credits: ESA Sub-surface ocean, chemical evolution? (Raulin et al., 2009) Mainly water ice and rocky material (Tobie et al., 2009) Credit: Cassini Radar Mapper, JPL, ESA, NASA Land-like surfaces spattered with lakes (Stofan et al., 2007) planet-like atmosphere. Absence of life: study prebiotic conditions and organic chemistry. Credits: NASA Credit: JPL, NASA Titan from UVIS

  24. Introduction – Why Titan’s atmosphere? Voyager 1, 1980 Cassini/Huygens 2004 Credits:JPL/NASA OBSERVATIONS LAB. EXPERIMENTS C2H2 C2H6 C2H4 H2 N2 CH4 (Kuiper, 1944) C7H8 Heavy ions Aerosols HCN C6H6 tholins MODELLING UV,VIS haze Organic? N2 and CH4 (destroyed) complex organic molecules and aerosol Credits:JPL/NASA General circulation, particle micro-physics, gas-solid relations. Variability: seasonal, latitudinal. What is the degree of complexity in the chemistry on Titan? How variable is it? Titan from UVIS

  25. Introduction – Cassini investigations INMS Ion and Neutral Mass Spectrometer 1500 km 1000 500 50 Surface UVIS Ultraviolet Imaging Spectrograph Abundances of atmospheric constituents. Vertical and horizontal distributions. Detect new molecules. Formation, composition and distribution of aerosols. Map global temperatures. Variability (seasonal effects) Expand in location and time the measurements of the atmosphere. CIRS Composite Infrared Spectrometer VIMS Visible and Infrared Mapping Spectrometer Credits: JPL/NASA Titan from UVIS

  26. UVIS stellar and solar occultations - UVIS instrument and data 563 – 1182 Å 19.4 Å resol.* 1115 – 1912 Å 4.8 Å resol.** * Extended source, occ. slit ** Extended source, low resol. Slit From Esposito et al. 2004 Titan from UVIS

  27. UVIS stellar and solar occultations - First steps in occultation analysis Geometry Tg altitude Titan FOV First steps (FUV, EUV): Dark Current Summing of rows Elimination of bad pixels Check light curves Altitude averaging … Titan from UVIS

  28. UVIS stellar and solar occultations - First steps in occultation analysis Tg altitude Titan Titan from UVIS

  29. UVIS stellar and solar occultations - Stellar vs. solar occultations Titan from UVIS

  30. UVIS/FUV stellar occultations – Absorption and transmission Absorption cross sections Transmission vs. altitude Transmission vs. wavelength Titan from UVIS

  31. UVIS/FUV stellar occultations – Column and number density retrieval (Press et al., 1996) Tikhonov regularization (Twomey, 1996) Complications: Column density and number density retrieval: ill-posed: solution `might’ exist but may not be unique nor stable. Column density: overdetermined problem. Non linear. Number densities: ill-conditioned (uncertainty amplification, oscillations). Linear. Titan from UVIS

  32. Retrieval methods and simulations – which species? Many species  abundance and ACS  absorption coefficient > 10-11 : 18 species worth a try Titan from UVIS

  33. Simulating stellar occultations – which species? 18 species, contribution to optical depth 11 species: CH4, C2H2, HCN, C2H4, C4H2, HC3N, C6H6, C4N2, CO, CH3, and AER 9 species: CH4, C2H2, HCN, C2H4, C4H2, HC3N, C6H6, CH3, and AER Titan from UVIS

  34. Simulating stellar occultations – retrieved column densities Titan from UVIS

  35. Benzene ACS in the VUV - Introduction Benzene ACS C6H6 present in large number of scientific contexts (aeronomy, astrophysics, biology, . . .) Titan from UVIS

  36. Benzene ACS in the VUV - Measurements Synchrotron radiation, BESSY II facility, Berlin. I, I0 Analysis process Titan from UVIS

  37. Benzene ACS in the VUV – More measurements Deuterium lamp radiation, Meudon Observatory facility, Meudon. Titan from UVIS

  38. Benzene ACS in the VUV – Results Synchrotron radiation, BESSY II facility, Berlin. 1A1g -> 1B1u Rydberg 1A1g -> 1E1u Titan from UVIS

  39. Benzene ACS in the VUV – More results Deuterium lamp radiation, Meudon Observatory facility, Meudon. Titan from UVIS

  40. Benzene ACS in the VUV – Results, temperature variation analysis Titan from UVIS

  41. UVIS/FUV stellar occultations - Previous work Shemansky et al., 2005. Flyby: Tb in Dec 2004. Koskinen et al., 2011. Flybys: T41 in Feb 2008; T53 in Apr 2009. Titan from UVIS

  42. UVIS/EUV solar occultations - Previous work 106 107 108 1091010 106 107 108 1091010 Vervack et al., 2004. Voyager 1/UVS. Flyby: Nov 1980. N2 and CH4. Temperature from N2 number densities. Global vertically averaged temperature profile (Snowden et al., 2013) (153 +/- 1) K Westlake et al., 2011 Titan from UVIS

  43. UVIS/EUV solar occultations – Instrument corrections Background correction Titan from UVIS

  44. UVIS/EUV solar occultations – General analysis Titan from UVIS

  45. UVIS/EUV solar occultations – Absorption and transmission Titan from UVIS

  46. UVIS/EUV solar occultations – Column and number density retrieval Tikhonov regularization (Twomey, 1996) Complications: Number density retrieval: ill-posed: solution `might’ exist but may not be unique nor stable. ill-conditioned (uncertainty amplification, oscillations). Linear. Titan from UVIS

  47. Temperature and variability – Temporal/Spatial coverage of data Titan from UVIS

  48. Abundance of mayor constituents (FUV stellar EUV solar occultations) Comparisons with previous measurements Titan from UVIS

  49. Temperature and variability – All flybys Titan from UVIS

  50. Temperature and variability Lon T vs. Lat LST T vs. time SLT Titan from UVIS

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