1. Titan UVIS Airglow Spectra: Modeling and Laboratory Studies
JOSEPH AJELLO
JPL
MICHAEL STEVENS
NRL
IAN STEWART
KRIS LARSEN
LARRY ESPOSITO
JOSH COLWELL
WILLIAM MCCLINTOCK
WAYNE PRYOR
GREG HOLSCLAW
LASP/CU

2. UVIS TITAN AIRGLOW PRIMARY GOALS
PRESENT FIRST CALIBRATED UV SPECTRA ( Å)
IDENTIFY SPECTRAL CONTENT -c'(0,0) 958Å?
IDENTIFY SOURCES BY MODEL SPECTRUM
PHOTODISSOCIATIVE IONIZATION EXCITATION (PDI)
PHOTOELECTRONS(PE) + N2
MULTIPLE SCATTERING IN c'(0,v'')PROGRESSION
MAGNETOSPHERIC ELECTRONS (ME)+ N2
ATOMIC N +e (PE or ME)
DEVELOP PE MODEL FOR 200 PERTURBED & STRONG RYDBERG BANDS N2 (b,b',c'-X)

3. CASSINI UVIS OBSERVATION
EUV/FUV AIRGLOW
& Å
1024 (spectral)x64 (spatial)
2.0 mrad x 59 mrad FOV
Inbound Orbit Tb 13dec04
105 km, 200 km resolution

4. EUV DAYGLOW OBSERVATION IN N2 RYDBERG BANDS (b 1Pu, b' 1Su, c 1Su  X 1Sg)
Dayside ( Å) 03:43 UT, 13DEC04
phase angle of 16.5o
distance 163,000km
Nightside 14:13 UT
163o phase angle
distance 50,500km
Resolution ~100 km

5. The EUV Airglow of Titan
However, (0,0) is optically thick near peak photoelectron exciation. Newer model results showed that (0,0) is weak and
many other features are there instead, including NI excited by photodissociative ionization.
UVIS data from December, 2004 now show the EUV airglow of Titan in detail.
(0,0) is indeed weak or absent and the
complexity of the spectrum is revealed.
Red curve is the composite of a four
component linear regression…
Titan V1 UVS airglow data suggested that the N2 c(0,0) and (0,1) bands dominated the EUV due to similarities with electron impact spectra from the lab.

6. Spectral Fitting of EUV Airglow
Electron impact laboratory spectrum without c(0,0-2).
Relative intensities of NI and NII PDI [Bishop and Feldman, 2003].
Relative intensities of (0,0-2) based on model results [Stevens, 2001].
HI Lyman- at 1026 Å fit separately.
Photon loss and redistribution in c(0)—X shown by comparing blue dotted and green lines.

7. COMPARISON CASSINI EUV TO LABORATORY SPECTRUM
5.6Å FWHM 5
Feature 6 100eV FWHM=0.2Å

8. COMPARIONS OF EUV DAGLOW & NIGHTGLOW SPECTRA (800-1140 Å) WITHIN SATURN MAGNETOSPHERE

9. IDENTIFICATION OF FUV SPECTRUM
Dayglow
900km
LBH 68R
HI 266R
NI 30R
CH4~1017cm2
Nightglow

10. GLOBAL MODEL OF N2 DISSOCIATION FOR FAST N (~1 eV) CHEMISTRY FROM EUV INTENSITY

11. MAJOR RESULTS OF UVIS 13DEC04 DAYGLOW ANALYSIS
c’(0,0) IS ABSENT, NI lines are present at 952, 964Å
MAIN EUV/FUV PROCESSES INVOLVE N2
PDI(XUV 5-410Å),
PE(e~23 eV),
PDE PROCESSES(XUV Å)
ALTITUDE OF EUV DAYGLOW 1100 KM
ALTITUDE OF FUV DAYGLOW 900 KM
EUV OUTPUT 2.9 X 107 WATTS-measure of Titan atmos. N2 Dissociation and fast N-atoms
FUV OUPUT (LBH) 3.6 X 107 WATTS-measure of Solar XUV input
FUV OUTPUT (NI,HI,CI) 1 X 108 WATTS
N ATOMS ~1 X 1027 GLOBAL ATOMS/S
MAGNETOSPHERE EXCITATION WEAKER BY ~20:1
UVS & UVIS IN GOOD CROSS CALIBRATION –SOLAR MAX/MIN~ 3:1
TECHNIQUE & CROSS SECTION FOR N2 PLANETARY ATMOSPHERES

12. COMPARISON OF VOYAGER UVS AND CASSINI UVIS - 24 YEARS APART