Titan Airglow Spectra From 2004 and 2008 and Laboratory Results for UVIS, ISS and VIMS (800-11,000 Å) JOSEPH AJELLO JPL JACQUES GUSTIN MICHAEL STEVENS IAN STEWART GREG HOLSCLAW JOSH COLWELL KRIS LARSEN LARRY ESPOSITO WILLIAM MCCLINTOCK WAYNE PRYOR

Tb MODEL, 2008 OBSERVATIONS AND LABORATORY RESULTS FOR TITAN UV-near IR OBSERVATIONS AND ANALYSIS AURIC FORWARD M ODEL ( VER )- UVIS D ATA C OMPARISON FUV L IMB P ROFILE ( KM) O RBIT T B AURIC FORWARD M ODEL ( VER )- UVIS D ATA C OMPARISON FUV L IMB P ROFILE ( KM) O RBIT T B UV-Visible-Optical-near IR (VOIR, Å ) N 2 AND H 2 E LECTRON IMPACT INDUCED LAB SPECTRA AT 20 AND 100 E LECTRON V OLTS F OR ISS AND VIMS UV-Visible-Optical-near IR (VOIR, Å ) N 2 AND H 2 E LECTRON IMPACT INDUCED LAB SPECTRA AT 20 AND 100 E LECTRON V OLTS F OR ISS AND VIMS M EDIUM R ESOLUTION (200 M Å FWHM) EUV Spectra and Emission Cross Sections of 300 Spectral Features of Electron Excited N 2 at 20 and 100 eV from Å M EDIUM R ESOLUTION (200 M Å FWHM) EUV Spectra and Emission Cross Sections of 300 Spectral Features of Electron Excited N 2 at 20 and 100 eV from Å 2008 EUV observations (199) thru DOY 340 with Solar Occultation port open-Strongest airglow spectrum to date 2008 EUV observations (199) thru DOY 340 with Solar Occultation port open-Strongest airglow spectrum to date

CASSINI UVIS OBSERVATION EUV/FUV AIRGLOW 2.0 (1.5)x59mrad FOV Inbound Orbit Tb 13dec04 Inbound Orbit Tb 13dec04 phase ang.16 o at 163,000km phase ang.16 o at 163,000km 10 5 km, 200 km resolution 10 5 km, 200 km resolution

Geometry Distant (13Dec04) UVIS FUV Limb Observation with Lower Atmosphere Scatter Light FOV= 1.5mR (0.09 o ) FOV= 1.5mR (0.09 o ) Scattered light FOV=.15 o ( FOV) Scattered light FOV=.15 o ( FOV) Total FOV=0.4 o Total FOV=0.4 o Distance =85,000 to 160,000 km Distance =85,000 to 160,000 km Limb rayheight = 1100 ±560 km Limb rayheight = 1100 ±560 km Contribution from 500 km to 1100 km spectrum transmitted thru CH 4 Contribution from 500 km to 1100 km spectrum transmitted thru CH 4 Solar incid.=70-90 o Solar incid.=70-90 o

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

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-  at 1215 Å. Regression Model

Regression Model Fits to Peak (1100 km) FUV Limb Dayglow Spectrum from 13Dec04 Regression Model 4- vectors Regression Model 4- vectors Rayleigh Scattering by N 2 Rayleigh Scattering by N 2 LBH Band system by N 2 + scattered LBH >1400 Å) LBH Band system by N 2 (+ scattered LBH >1400 Å) NI lines PDI by N 2 NI lines PDI by N 2 H Ly  solar fluorescence by H, … H Ly  solar fluorescence by H, …

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

Auric Model of Titan Limb LBH Profile

LBH Limb Profile for Orbit Tb and CH 4 absorption at 1356 Å along peak LOS AURIC Model vs UVIS Limb Profile LBH optical depth at 1100km MRH for strongest (3,0) band

Analysis of the NI FUV Emissions A Simpler Calculation 1)no predissociation and no cascade. 2) Peak brightness afactor of seven > than observations 3) Disk Brightness only >56% brighter

From January Team Meeting Nitrogen Day/Night Kris Larsen Results Dayside atomic Nitrogen: ± kR Nightside Atomic Nitrogen: ± kR Dayside Nitrogen LBH: ± kR Nightside Nitrogen LBH: ± kR Little to no day to nightside correlation (R 2 < 0.3)

FUV Observation at 50 km over Full Spectral Range of UVIS ( Å) Rayleigh Scattering tends to 10 3 LBH Intensity Rayleigh Scattering tends to 10 3 LBH Intensity

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

MAJOR RESULTS OF UVIS 13DEC04 LIMB DAYGLOW ANALYSIS ALTITUDE OF FUV DAYGLOW 1100 KM ALTITUDE OF FUV DAYGLOW 1100 KM RAYLEIGH SCATTERING TOPSIDE ~500 km RAYLEIGH SCATTERING TOPSIDE ~500 km ENHANCE LBH ENHANCE LBH SECOND SPECTROSCOPIC EVIDENCE FOR THOLINS (LIANG ET AL.2007) SECOND SPECTROSCOPIC EVIDENCE FOR THOLINS (LIANG ET AL.2007) FIRST GEOMETRIC ALBEDO OF TITAN ( Å) FIRST GEOMETRIC ALBEDO OF TITAN ( Å) Factor of 4 disagreement –model vs data Factor of 4 disagreement –model vs data 2 GRL publications + 1 (in progress) 2 GRL publications + 1 (in progress)

VOIR LABORATORY STUDIES OF ELECTRON EXCITED N 2 AND H 2 FROM Å FOR ISS AND VIMS DARKSIDE AIRGLOW OBSERVATIONS OF TITAN EUV STUDIES OF N 2 FOR UVIS Å

VOIR ELECTRON EXCITED N 2 SPECTRUM AT 25 eV

VOIR ELECTRON EXCITED N 2 SPECTRUM AT 100 eV

H 2 VOIR Emission Spectrum by Electron Impact Fluorescence for VIMS & ISS Energy level Diagram e (100 eV) H 2  h ( Å)

Medium Resolution Study (200 mÅ FWHM) of N 2 EUV Spectrum from Å by e-Impact Identified 288 N 2 molecular bands & N I,I atomic multiplets (update Ajello et al., 1989) Identified 288 N 2 molecular bands & N I,I atomic multiplets (update Ajello et al., 1989)

N 2 Pressure Studies at Medium Spectral Resolution in the EUV

Medium Resolution Study of N 2 Emission Spectrum at 100 eV Electron Impact Energy -Over plot of 20 e V and 100 eV spectra to identify NI atomic Multiplets and Molecular bands -ID 288 features at sufficient resolution to resolve vibrational transition or atomic line -Measured Emission Cross Section and correct resonance bands for pressure

Identification of c ’ 4( 0, 6- 13) Vibrational Levels in Electron Impact Fluorescence (Bishop et al., 2006) -First Labortory Spectra at 200 mÅ FWHM by e-Impact showing high c ’ 4 (v’=0,v’’ 6-13 levels) -past analysis has not studied role of c ’ 4( 0, 7-13) Vibrational Levels (~1 x cm 2 ) -Observed by FUSE on Earth Dayglow

2008 EUV TITAN AIRGLOW OBSERVATIONS WITH SOLAR OCCULTATION PORT OPEN QUICK-LOOK ANALYSIS OF OBSERVATIONS AND COMPARISON TO Tb (2004)

199 EUV Observations of Titan in 2008 thru DOY340 with Brightest c’ 4 Bands 199 EUV Observations of Titan in 2008 thru DOY340 with Brightest c’ 4 Bands

Comparison of 2004 and 2008 Calibrated Titan Airglow EUV Spectra with ID

Comparison of Orbit Tb (2004) Signal + Mesa with Brightest EUV Titan Airglow Spectrum in 2008

GEOMETER Image of EUV2008_133_04_40_59_UVIS_067TI_ MEDRESDRK001_VIMS

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