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

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

• Stellar and solar occultations in EUV and FUV using Cassini UVIS• Probes region between 300 to

1500km

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

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

• Choice of occultation data sets• Pointing drift can be major

issue

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

• Choice of occultation data sets• Pointing drift can be major

issue

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

• Choice of occultation data sets• Pointing drift can be major

issue

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

• Choice of occultation data sets• Pointing drift can be major

issue

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

• Choice of occultation data sets• Pointing drift can be major

issue

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

• Choice of occultation data sets• Pointing drift can be major

issue

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

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

• Methodology• Grid search of parameters

• Only 2 species in retrieval• Can calculate χ2 surface• Marginalized posteriors

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

• Methodology• Grid search of parameters

• Only 2 species in retrieval• Can calculate χ2 surface• Marginalized posteriors

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

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

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

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

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

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

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

• Useful for comparison, but really want to measure densities• Inverse Abel transform

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

• Interpolated density profiles• 1-σ error region

• Nitrogen profiles appear to vary• Wave like structure?

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

• “Mean” state of atmosphere• How does this compare to INMS?

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

• INMS data for T26, T32, and T41• Westlake et al., 2011

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

• 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. DPS 44th Meeting, 2012Nitrogen Chemistry in Titan’s Upper Atmosphere

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