Nitrogen Chemistry in Titan’s Upper Atmosphere

1. Nitrogen Chemistry in Titan’s Upper Atmosphere J. A. Kammer†, D. E. Shemansky‡, X. Zhang†, and Y. L. Yung† †California Institute of Technology, Pasadena, CA ‡Space Environment Technologies, Pasadena, CA DPS 44th Meeting Reno, NV Oct. 17, 2012

2. Stellar and solar occultations in EUV and FUV using Cassini UVIS • Probes region between 300 to 1500km J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

3. Stellar and solar occultations in EUV and FUV using Cassini UVIS • Probes region between 300 to 1500km • Everything starts at the top • Photochemistry drives production of hydrocarbons, haze particles J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

4. Stellar and solar occultations in EUV and FUV using Cassini UVIS • Probes region between 300 to 1500km • Everything starts at the top • Photochemistry drives production of hydrocarbons, haze particles • Previous work (Koskinen et al., 2011) examined FUV lightcurves • EUV complementary source of information – N2 and CH4 J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

5. Stellar and solar occultations in EUV and FUV using Cassini UVIS • Probes region between 300 to 1500km • Everything starts at the top • Photochemistry drives production of hydrocarbons, haze particles • Previous work (Koskinen et al., 2011) examined FUV lightcurves • EUV complementary source of information – N2 and CH4 • Composition and temperature results from both solar and stellar observations J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

6. Choice of occultation data sets • Pointing drift can be major issue J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

7. Choice of occultation data sets • Pointing drift can be major issue J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

8. Choice of occultation data sets • Pointing drift can be major issue J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

9. Choice of occultation data sets • Pointing drift can be major issue J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

10. Choice of occultation data sets • Pointing drift can be major issue J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

11. Choice of occultation data sets • Pointing drift can be major issue J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

12. Choice of occultation data sets • Pointing drift can be major issue • Out of ~25 total observations made by UVIS, selected: • Four stellar occultations during T21, T35, and T41 (ingress and egress) • Two solar occultations (T10, T53) J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

13. Forward model of optical depth • Cross sections for N2 and CH4 • Windowed EUV region from about 900 to 1100 angstroms J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

14. Forward model of optical depth • Cross sections for N2 and CH4 • Windowed EUV region from about 900 to 1100 angstroms J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

15. Methodology • Grid search of parameters • Only 2 species in retrieval • Can calculate χ2 surface • Marginalized posteriors J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

16. Methodology • Grid search of parameters • Only 2 species in retrieval • Can calculate χ2 surface • Marginalized posteriors J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

17. J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

18. J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

19. J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

20. J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

21. J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

22. J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

23. Useful for comparison, but really want to measure densities • Inverse Abel transform J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

24. Interpolated density profiles • 1-σ error region • Nitrogen profiles appear to vary • Wave like structure? J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

25. “Mean” state of atmosphere • How does this compare to INMS? J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

26. INMS data for T26, T32, and T41 • Westlake et al., 2011 J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

27. Effective temperatures from hydrostatic fits to geopotential height for N2 • Widely varying temperatures: • T10: 184K – T21: 153K – T35: 218K • T41: 136K – T41: 124K – T53: 160K J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012

28. Summary • EUV observations complementary to FUV hydrocarbon profiles • Some difficulties due to pointing • Simple process to convert lightcurves to abundances, then densities • Comparison to INMS • Effective temperatures from hydrostatic fits to geopotential height for N2 J. A. Kammer et al. Nitrogen Chemistry in Titan’s Upper Atmosphere DPS 44th Meeting, 2012