Titan: FUV Limb Spectra From 2004
and EUV Laboratory Cross Sections
and 2007-9 Observations
JOSEPH AJELLO
JPL
MICHAEL STEVENS
NRL
JACQUES GUSTIN
LPAP
GREG HOLSCLAW
CU
TODD BRADLEY
UCF
TB LIMB MODEL, RECENT LAB ANALYSIS & UVIS
OBSERVATIONS
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SUBMITTED FUV LIMB PAPER (TB) SCIENCE
“Production of Titan’s Far Ultraviolet N2
AURIC MODEL ADAPTED TO TITAN – (FORWARD MODEL
VERS-SUCCESSFULLY USED ON EARTH TIMED)- UVIS DATA
COMPARISON FUV LIMB PROFILE (~15%)
Used AURIC to identify ‘mystery line(s)
2007-9 EUV (375) observations (MAY07-FEB09) with
Solar Occultation port open-TENTATIVE ID OF 833 Å
feature
MEASURED 100 eV CROSS SECTION AND IDENTIFIED 288
EMISSION FEATURES FROM 800-1350 Å In Laboratory
The FUV Airglow of Titan
Titan FUV UVIS Airglow Limb Spectra from
the Surface to Exosphere on 13Dec04.
Spectral Fitting of FUV Airglow
In Upper Atmosphere (1050 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 ( note deficits at 1622, 1657, 1687, 1726 Å)
NRL Analysis without solar scattering UVIS airglow
observations at a tangent altitude of 1150±50 km above
Titan’s surface on 13 Dec 2004
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A) Composite fit in red. The dash curve shows the highaltitude UVIS spectrum background.
B) Residual UVIS spectrum after subtraction of the
background, including H Ly a
NEW TITAN AURORAL Atmospheric Ultraviolet Radiance
Integrated Code (AURIC) MODEL
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A) VPRs for LBH and NI spectral features (Dashed lines -N2 LBH (black) and N I (red)
emissions disk (solar incidence angle 51°). Solid lines limb observations at (82°).
B) UVIS limb observations of LBH (black dots) and N I (red dots) emissions.
SUMMARY OF Tb LIMB MODEL &
OBSERVATIONAL INTENSITIES1
Observed Calculated
Observed Calculated
Peak
Disk
Disk
(Calc. -
Radiance
Radiance
Obs)/Obs
(R)
(R)2
Limb
Radiance
(R)
10.0
9.2
(Calc. –
Peak
d Peak
Obs)/Obs
Altitude
Altitude
(km)
(km)
Calc. –
Limb
Obs.
Radiance
(km)
(R)
1050 
13.63
-8%
LBH1
-12%
2.3
8.3
9.2
+11%
1007
-43
1012
-138
280
17.2 
NI
1
Calculate
15.4 
N2
PDI1
Observed
Peak
1150
13.9
-19%
2.6
All observations and calculations integrated between 1160-1365 Å.
280
MYSTERY FUV FEATURES :
N2 VK system (rather than C I line at 1657 A, and Mystery
Line at 1597 , etc)?
Major result:
Mystery FUV
Features are
Not
Solar lines or
C I Airglow
Comparison of UVIS FUV Spectra at 950 and
1150 km Showing Indication of VK Bands
MAJOR RESULTS OF UVIS
13DEC04 LIMB DAYGLOW
ANALYSIS
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ALTITUDE OF FUV DAYGLOW 1150 KM
RAYLEIGH SCATTERING TOPSIDE ~500 km
JAN09-Factor of 4 disagreement –model vs
data- is gone
JAN10- model limb radiances agree with
UVIS limb & disk intensities
Sun drives the Titan dayglow, Tb.
Mystery Ariglow Line(s) are N2 (VK) not C I
2007-9 EUV TITAN AIRGLOW
OBSERVATIONS WITH SOLAR
OCCULTATION PORT OPEN
QUICK-LOOK ANALYSIS OF
DARKSIDE AND BRIGHT SIDE
OBSERVATION 800-1150 Å
375 EUV Observations of Titan 2007-9
with Bright 1085 Å or c’4 Bands
Comparison of Orbit Tb (2004) Signal +
Mesa with Brightest EUV Titan Airglow
Spectrum in 2008
DARK SIDE OBSERVATION OF TITAN ON
25MARCH2008
MODEL OF 25MARCH2009 DARKSIDE
OBSERVATION: TENTATIVE ID O II(833A)
?
?
T. Cravens, Oct. 09
Possible Method of Producing Excited O+(834 Å ) at Titan
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Excitation of O (or O+), or other oxygen-bearing species (CO, H2O, ...) by supratheramal electrons is
unlikely since the fraction of such species is not likely to be more than 1 part in 10 4 (Horst et al.,
Cravens et al., 08, Icarus-less than .001 R.)
Following the ion precip paper (Cravens et al., 08, GRL), the following processes might work:
1. O(fast) + N2 -> O+* + N2 + e
(e-loss with excitation) (O comes from charge exchange of
precipitating O+)
2. O+(fast) + N2 -> O+* + N2
(direct excitation)
3. O++(fast) + N2 -> O+* + N2+ (charge exchange with excitation-(O++ comes from electron loss of
O+ with N2)
(1) and (2) ;The first two processes could produce about 1 - 3 R for T5. For T5, Titan was in the
plasma sheet. For more typical passes, divide by 10 (i.e., 0.1 0.3 R with optimistic efficiencies).
(3) The third process I estimated even more crudely but it could also give0.1-1 R (T5) or less for nonT5. But a 10-20% efficiency for excitation is more likely here than for the first two.
Bottom line OII 834 A emission could possibly be produced with the 0.3 R intensity observed by
energetic oxygen precipitation. With the 10-20% efficiency they definitely would be, but with much
lower efficiencies then no. Another question would then be why are other OI and OII in the 800- 1000
A part of the spectrum not also being produced or seen?
HIGH RESOLTUION STUDY OF EUV ELECTROM IMPACT
INDUCED FLUORESCENCE SPECTRUM OF N2
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Pressure study to identify resonance
bands and rotational temperature
dependence (175-300 K)
Identify all 288 features in electron
impact fluorescence (800-1350 Å )
Determine emission cross section for
each feature for AURIC modeling
COMPARISON CASSINI EUV TO
LABORATORY SPECTRUM
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5
5.6Å FWHM
Feature 6
100eV
FWHM=0.2Å
DETERMINATION OF RESONANCE BANDS OF N2 WITH
HIGH RESOLUTION SPECTROSCOPY
DDl=0.2AÅ
CONTINUATION OF PRESSSURE STUDY OF EUV
SPECTRUM OF N 2 & STUDY OF c’4(0,v”) progression
High Resolution Laboratory
Spectroscopy of N2 at 0.1 Å FWHM
and ID of each feature
The 100 eV Medium Resolution Electron Impact Induced
Fluorescence Spectrum Identifications of N2 from 1050-1100 Å
1
2
3
4
1050.13
1050.81
1051.53
1052.49
1050.61
1050.93
1052.21
1053.13
1050.81
1051.53
1052.49
1053.65
0.78
0.76
3.15
3.84
1050.69
1050.69
1052.57
1052.68
1053.337
1053.656
1053.433
c'4(0,4) P-branch
c'4(0,4) R-branch
c'4(1,5)
c'4(2,6)s
c'4(4,8)
NI(2Do4F, 4P, 2P)
5
1053.65
1053.97
1054.41
1.00
6
7
8
9
10
11
12
1054.41
1055.13
1056.73
1059.09
1063.01
1065.25
1066.17
1054.77
1055.49
1057.73
1059.33
1064.13
1065.85
1066.69
1055.13
1056.73
1059.09
1060.61
1064.77
1066.17
1066.85
0.37
2.30
12.75
2.14
0.63
0.81
1.77
1054.430
1055.44
1057.63
1059.28
1064.01
1065.66
1066.36,
1066.71
NI(2Do4P)
b(7,5)
b(1,3)
b'(12,8)
b(5,6)
b'(8,7)
b'(5,6), weak
b'(11,8)vs
13
1066.85
1067.65
1068.17
7.74
1066.99
1067.95
NI(2Do2,4D)
14
1068.17
1068.69
1068.93
3.53
1068.31,
1068.2211068.681
b'(14,9)weak
NI(2Do2,4P, 2,4F)
15
1068.93
1069.17
1069.77
2.10
16
1069.77
1070.01
1070.29
1.04
1069.468
1069.626
1069.990
1070.01,
1070.11
NI(2Do2P)
NI(3Po3D)
NI(2Do2P)
NI(2Do4P)
NI(2Do4P)
17
1070.29
1071.05
1071.61
0.82
1070.96
o3(4,9)
18
19
20
1072.21
1074.41
1076.85
1072.57
1076.01
1077.21
1073.01
1076.85
1077.49
0.38
2.61
1.30
1072.43
1075.73
1077.15
1077.20
1077.33
1077.36
b'(7,7)
c'4(0,5)
c'4(2,7)
c'4(4,9)
c'4(3,8)
c'4(1,6)
21
1077.49
1078.05
1079.29
3.49
1078.18
b'(16,10)
9 Electronic States Contribute to
EUV Spectrum at Titan
Electronic Transition
c4' 3ps 1S+u X 1S+g
Rydberg
b' 1S+u X 1S+g valence
b 1Pu X 1S+g -valence
o3 3ss 1PuX 1S+g core excited
c5' 4ps 1S+u X 1S+g
c6' 5ps 1S+u X 1S+g
c4 4pp 1Pu X 1S+g
c5 4ss or 5pp 1PuX
1S +
g
c3 3pp 1Pu X 1S+g
3dp 1S+u (0)X 1S+g
(0,1)-core excited?
1S+ (0) X 1S+ (0,1) ?
u
g
Electronic Cross Section
(this work)
1191
Te
52.2
104498
85.4
5.7
101675
105869
2.6
4.8
~0.
11.7
115876
7.4
1.5
104476
1.5
notes
-1)
(cm
104519
115635.9
Converges to N2+ X
2S+ (v=0)
g