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**JOSEPH AJELLO**

**JPL**

**JACQUES GUSTIN**

**IAN STEWART**

**KRIS LARSEN**

**LARRY ESPOSITO**

**WILLIAM **

**MCCLINTOCK**

**WAYNE PRYOR**

**GREG HOLSCLAW**

**EUV/FUV AIRGLOW**

**2.0 (1.5)x59mrad FOV**

**Inbound Orbit Tb 13dec04 phase ang.16**

**o at **

**163,000km**

**10 5 km, 200 km resolution**

**The FUV Airglow of Titan**

**Titan FUV UVIS Airglow Limb Spectra from the Surface to Exosphere on 13Dec04.**

Regression Spectral Analysis of UVIS FUV

Disk Dayglow Spectrum from 13Dec04

**Regression Model 4-vectors**

**Rayleigh Scattering by N**

**2**

**LBH Band system by N**

**2**

**NI lines PDI by N**

**2**

H Ly a solar fluorescence by H, …

**mixing ratios obtained from fit of UVIS reflected sunlight spectrum of Titan (1500-1880 Å).**

5.4 x 10 -8

2.4 x 10 -6

3.6 x 10 -5 6.9 x 10 -6

1.1 x 10 -8

Liang et al., 2007 tholins

7.7 x 10 -7

N

2 density is ~ 1 x10 16 cm -3 at 300 km.

Tholin mixing ratio is then ~ 1 x 10 -11

A plot of the geometric albedo of Titan from 1500 to 11000 Å

**(adapted from Mckay et al., 2001)**

**The FUV Airglow of Titan**

**Titan FUV UVIS Airglow Limb Spectra from the Surface to Exosphere on 13Dec04.**

Key Altitude Limb Profiles for the 13Dec2004 Titan

Observations

**LBH**

**NI 1493 Å**

**SOLAR**

**REFLECTANCE**

**16001900 Å**

H Ly a

**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 Ratio **

**@ at each altitude: f f f c2H2 c2H4 c4H2**

**Tholins**

**(e.g.C**

**11**

**H**

**11**

**N**

**2**

**)**

**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 Lymana at 1215 Å.**

**• Regression Model**

**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**

Regression Model Fits to Peak (1100 km)

FUV Limb Dayglow Spectrum from 13Dec04

**Regression Model 4vectors**

**Rayleigh Scattering by N**

**2**

**LBH Band system by N**

**2 scattered LBH >1400 Å)**

**(+ **

**NI lines PDI by N**

**2**

**H Ly a solar fluorescence by **

**H, …**

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

**Geometry Distant (13Dec04) UVIS FUV Limb **

**Observation with Lower Atmosphere Scatter Light**

**FOV= 1.5mR (0.09**

**o )**

**Scattered light **

**FOV=.15**

**o ( 10 -3 FOV)**

**Total FOV=0.4**

**o **

**Distance =85,000 to **

**160,000 km**

**Limb rayheight = **

**1100 ± 560 km**

**Contribution from **

**500 km to 1100 km spectrum transmitted thru **

**CH**

**4 t slant**

**CH**

**4**

(1)~

**10 16 cm -2 for **

**(1200km) at 1300Å**

Regression Model Fit to Middle Atmosphere FUV

Limb Dayglow Spectrum (Liang et al., 2007)

**Compare Liang et al., 2007**

**C**

**4**

**H**

**2**

**C**

**2**

**H**

**4**

**CH**

**4**

**C**

**2**

**C**

**2**

**H**

**2**

**H**

**6**

**= [4.5e15**

**]**

**= [4.0e16]**

**= [6.0e19]**

**= [2.1e17]**

**= [7.0e16]**

**HCN = [1.0e17**

**]**

**Regression Model 4-vectors**

**Rayleigh Scattering by N**

**2**

**LBH Band system by N**

**2**

**NI lines PDI by N**

**2**

**H Ly a solar fluorescence by H, …**

**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 Ly a increases with altitude (~doubles)

Mystery Line Needs Lower

Atmosphere Source

CI strong to Ionosphere

**FUV Observation at 50 km over Full Spectral **

**Range of UVIS (1150-1850 Å)**

Rayleigh Scattering tends to 10 3 LBH Intensity

**Mixing Ratios Obtained from Fit of UVIS reflected sunlight spectrum at Limb of Titan **

**(study at 1500-1880 Å).**

**ALTITUDE OF FUV DAYGLOW 1100 KM**

**RAYLEIGH SCATTERING TOPSIDE ~500 km**

**ENHANCED LBH INTENSITY @IONOSPHERE **

**(instrumental or real) **

**SECOND SPECTROSCOPIC EVIDENCE FOR **

**THOLINS **

**(LIANG ET AL.2007)**

**FIRST GEOMETRIC ALBEDO OF TITAN (1500-1900 **

**Å) **

**MYSTERY LINE AND CI FEATURES STRONG IN **

**LOWER ATMOSPHERE**

**2 GRL publications + 1 on Limb (in progress)**