1. Titan Airglow FUV Limb Spectra From Cassini UVIS Observations
JOSEPH AJELLO
JPL
JACQUES GUSTIN
IAN STEWART
KRIS LARSEN
LARRY ESPOSITO
WILLIAM MCCLINTOCK
WAYNE PRYOR
GREG HOLSCLAW
team meeting: june 2008

2. CASSINI UVIS OBSERVATION
Inbound Orbit Tb 13dec04
phase ang.16o at 163,000km
105 km, 200 km resolution
EUV/FUV AIRGLOW
2.0 (1.5)x59mrad FOV

3. The FUV Airglow of Titan
Titan FUV UVIS Airglow Limb Spectra from the Surface to Exosphere on 13Dec04.

4. Regression Spectral Analysis of UVIS FUV Disk Dayglow Spectrum from 13Dec04
Regression Model 4-vectors
Rayleigh Scattering by N2
LBH Band system by N2
NI lines PDI by N2
H Lya solar fluorescence by H, …

5. mixing ratios obtained from fit of UVIS reflected sunlight spectrum of Titan (1500-1880 Å).
Liang et al., 2007
tholins
7.7 x 10-7
N2 density is ~ 1 x1016 cm-3 at 300 km.
Tholin mixing ratio is then ~ 1 x 10-11

6. A plot of the geometric albedo of Titan from 1500 to 11000 Å (adapted from Mckay et al., 2001)

7. The FUV Airglow of Titan
Titan FUV UVIS Airglow Limb Spectra from the Surface to Exosphere on 13Dec04.

8. Key Altitude Limb Profiles for the 13Dec2004 Titan Observations
NI 1493 Å
LBH
SOLAR
REFLECTANCE Å
H Ly a

9. Model Long Wavelength (1500-1900 Å) FUV Reflected Solar Light (step 1 - Vector 1)
solar reflection model at Limb (Lommel-Seeliger) law
Modeling Parameter is
Strong Absorber Mixing at each altitude:
fc2H2
fc2H4
fc4H2
Tholins
(e.g.C11H11N2)

10. Spectral Fitting of FUV Airglow In Lower Atmosphere (100 km)
Electron impact 18 eV laboratory spectrum.
Relative intensities of NI and NII PDI [Bishop and Feldman, 2003].
Rayleigh Scattering
HI Lyman-a at 1215 Å.
Regression Model

11. Spectral Fitting of FUV Airglow In Middle Atmosphere (500 km)
Electron impact 18 eV laboratory spectrum.
Relative intensities of NI and NII PDI [Bishop and Feldman, 2003].
Rayleigh Scattering
HI Lyman-a at 1215 Å.
Regression Model

12. Regression Model Fits to Peak (1100 km) FUV Limb Dayglow Spectrum from 13Dec04
Regression Model 4-vectors
Rayleigh Scattering by N2
LBH Band system by N2 (+ scattered LBH >1400 Å)
NI lines PDI by N2
H Lya solar fluorescence by H, …

13. Laboratory Spectrum and Model of LBH Band system by 18 eV Electrons

14. Geometry Distant (13Dec04) UVIS FUV Limb Observation with Lower Atmosphere Scatter Light
FOV= 1.5mR (0.09o)
Scattered light FOV=.15o (10-3 FOV)
Total FOV=0.4o
Distance =85,000 to 160,000 km
Limb rayheight = 1100 ±560 km
Contribution from 500 km to 1100 km spectrum transmitted thru CH4
tslant(1)~1016 cm-2 for CH4 (1200km) at 1300Å

15. Regression Model Fit to Middle Atmosphere FUV Limb Dayglow Spectrum (Liang et al., 2007)
Compare Liang et al., 2007
C4H2 = [4.5e15]
C2H4 = [4.0e16]
CH4 = [6.0e19]
C2H2 = [2.1e17]
C2H6 = [7.0e16]
HCN = [1.0e17]
Regression Model 4-vectors
Rayleigh Scattering by N2
LBH Band system by N2
NI lines PDI by N2
H Lya solar fluorescence by H, …

16. Minimum Ray Height Altitude Profiles of Important Emissions from Cassini UVIS 13Dec04
LBH bands Peak altitude is 1100 km
Rayleigh Scattering topside is 500 km
H Lya increases with altitude (~doubles)
Mystery Line Needs Lower Atmosphere Source
CI strong to Ionosphere

17. Rayleigh Scattering tends to 103 LBH Intensity
FUV Observation at 50 km over Full Spectral Range of UVIS ( Å)
Rayleigh Scattering tends to 103 LBH Intensity

18. Mixing Ratios Obtained from Fit of UVIS reflected sunlight spectrum at Limb of Titan (study at Å).

19. MAJOR RESULTS OF UVIS 13DEC04 LIMB DAYGLOW ANALYSIS
ALTITUDE OF FUV DAYGLOW 1100 KM
RAYLEIGH SCATTERING TOPSIDE ~500 km
ENHANCED LBH (instrumental or real)
SECOND SPECTROSCOPIC EVIDENCE FOR THOLINS (LIANG ET AL.2007)
FIRST GEOMETRIC ALBEDO OF TITAN ( Å)
MYSTERY LINE AND CI FEATURES STRONG IN LOWER ATMOSPHERE
2 GRL publications + 1 on Limb (in progress)