Titan: FUV Limb Spectra From 2004 and EUV Laboratory Cross Sections and Observations JOSEPH AJELLO JPL MICHAEL STEVENS NRL JACQUES GUSTIN LPAP GREG HOLSCLAW CU TODD BRADLEY UCF

T B LIMB MODEL, RECENT LAB ANALYSIS & UVIS OBSERVATIONS SUBMITTED FUV LIMB PAPER (T B ) SCIENCE “Production of Titan’s Far Ultraviolet N 2 SUBMITTED FUV LIMB PAPER (T B ) SCIENCE “Production of Titan’s Far Ultraviolet N 2 AURIC M ODEL A DAPTED TO T ITAN – ( FORWARD M ODEL VERS - SUCCESSFULLY USED ON EARTH TIMED)- UVIS D ATA C OMPARISON FUV L IMB P ROFILE (~15%) AURIC M ODEL A DAPTED TO T ITAN – ( FORWARD M ODEL VERS - SUCCESSFULLY USED ON EARTH TIMED)- UVIS D ATA C OMPARISON FUV L IMB P ROFILE (~15%) Used AURIC to identify ‘mystery line(s) Used AURIC to identify ‘mystery line(s) EUV (375) observations (MAY07-FEB09) with Solar Occultation port open-TENTATIVE ID OF 833 Å feature EUV (375) observations (MAY07-FEB09) with Solar Occultation port open-TENTATIVE ID OF 833 Å feature M EASURED 100 eV CROSS SECTION AND IDENTIFIED 288 EMISSION FEATURES FROM Å In Laboratory M EASURED 100 eV CROSS SECTION AND IDENTIFIED 288 EMISSION FEATURES FROM Å In Laboratory

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

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-  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 A) Composite fit in red. The dash curve shows the high- altitude UVIS spectrum background. A) Composite fit in red. The dash curve shows the high- altitude UVIS spectrum background. B) Residual UVIS spectrum after subtraction of the background, including H Ly  B) Residual UVIS spectrum after subtraction of the background, including H Ly 

NEW TITAN AURORAL Atmospheric Ultraviolet Radiance Integrated Code (AURIC) MODEL 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°). 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. B) UVIS limb observations of LBH (black dots) and N I (red dots) emissions.

Observed Disk Radiance (R) Calculated Disk Radiance (R) 2 (Calc. - Obs)/Obs Observed Peak Limb Radiance (R) Calculated Peak Limb Radiance (R) (Calc. – Obs)/Obs Observed Peak Altitude (km) Calculate d Peak Altitude (km) Calc. – Obs. (km) N 2 LBH % 15.4  % 1050  N I PDI % 17.2  % 1150  All observations and calculations integrated between Å. SUMMARY OF Tb LIMB MODEL & OBSERVATIONAL INTENSITIES 1

MYSTERY FUV FEATURES : N2 VK system (rather than C I line at 1657 A, and Mystery Line at 1597, etc)? 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 ALTITUDE OF FUV DAYGLOW 1150 KM ALTITUDE OF FUV DAYGLOW 1150 KM RAYLEIGH SCATTERING TOPSIDE ~500 km RAYLEIGH SCATTERING TOPSIDE ~500 km JAN09-Factor of 4 disagreement –model vs data- is gone JAN09-Factor of 4 disagreement –model vs data- is gone JAN10- model limb radiances agree with UVIS limb & disk intensities JAN10- model limb radiances agree with UVIS limb & disk intensities Sun drives the Titan dayglow, Tb. Sun drives the Titan dayglow, Tb. Mystery Ariglow Line(s) are N 2 (VK) not C I Mystery Ariglow Line(s) are N 2 (VK) not C I

EUV TITAN AIRGLOW OBSERVATIONS WITH SOLAR OCCULTATION PORT OPEN QUICK-LOOK ANALYSIS OF DARKSIDE AND BRIGHT SIDE OBSERVATION Å

375 EUV Observations of Titan with Bright 1085 Å or c’ 4 Bands 375 EUV Observations of Titan 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 T. Cravens, Oct. 09 Possible Method of Producing Excited O + (834 Å ) at Titan 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.) 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: Following the ion precip paper (Cravens et al., 08, GRL), the following processes might work: 1. O(fast) + N 2 -> O+* + N 2 + e (e-loss with excitation) (O comes from charge exchange of precipitating O+) 1. O(fast) + N 2 -> O+* + N 2 + e (e-loss with excitation) (O comes from charge exchange of precipitating O+) 2. O + (fast) + N 2 -> O+* + N 2 (direct excitation) 2. O + (fast) + N 2 -> O+* + N 2 (direct excitation) 3. O ++ (fast) + N 2 -> O+* + N 2 + (charge exchange with excitation-(O ++ comes from electron loss of O + with N 2 ) 3. O ++ (fast) + N 2 -> O+* + N 2 + (charge exchange with excitation-(O ++ comes from electron loss of O + with N 2 ) (1) and (2) ;The first two processes could produce about 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). (1) and (2) ;The first two processes could produce about 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 non- T5. But a 10-20% efficiency for excitation is more likely here than for the first two. (3) The third process I estimated even more crudely but it could also give0.1-1 R (T5) or less for non- T5. 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 A part of the spectrum not also being produced or seen? 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 A part of the spectrum not also being produced or seen?

HIGH RESOLTUION STUDY OF EUV ELECTROM IMPACT INDUCED FLUORESCENCE SPECTRUM OF N 2 Pressure study to identify resonance bands and rotational temperature dependence ( K) Pressure study to identify resonance bands and rotational temperature dependence ( K) Identify all 288 features in electron impact fluorescence ( Å ) Identify all 288 features in electron impact fluorescence ( Å ) Determine emission cross section for each feature for AURIC modeling Determine emission cross section for each feature for AURIC modeling

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

DETERMINATION OF RESONANCE BANDS OF N 2 WITH HIGH RESOLUTION SPECTROSCOPY  AÅ

CONTINUATION OF PRESSSURE STUDY OF EUV SPECTRUM OF N 2 & STUDY OF c’ 4 (0,v”) progression

High Resolution Laboratory Spectroscopy of N 2 at 0.1 Å FWHM and ID of each feature

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( 2 D o  4 F, 4 P, 2 P) NI( 2 D o  4 P) b(7,5) b(1,3) b'(12,8) b(5,6) b'(8,7) , b'(5,6), weak b'(11,8)vs NI( 2 D o  2,4 D) , b'(14,9)weak NI( 2 D o  2,4 P, 2,4 F) NI( 2 D o  2 P) NI( 3 P o  3 D) , NI( 2 D o  2 P) NI( 2 D o  4 P) o 3 (4,9) b'(7,7) c' 4 (0,5) c' 4 (2,7) c' 4 (4,9) c' 4 (3,8) c' 4 (1,6) b'(16,10) The 100 eV Medium Resolution Electron Impact Induced Fluorescence Spectrum Identifications of N 2 from Å

9 Electronic States Contribute to EUV Spectrum at Titan Electronic Transition Electronic Cross Section (this work) T e ( cm - 1) notes c 4 ' 3p  1   u  X 1   g Rydberg Converges to N 2 + X 2   g (v=0) b' 1   u  X 1   g - valence b 1  u  X 1   g -valence o 3 3s  1  u  X 1   g - core excited c 5 ' 4p  1   u  X 1   g c 6 ' 5p  1   u  X 1   g 4.8 c 4 4p  1  u  X 1   g ~ c 5 4s  or 5p  1  u  X 1   g 11.7 c 3 3p  1  u  X 1   g d  1   u (0)  X 1   g (0,1)-core excited?   u (0)  X 1   g (0,1) ? 1.5