R. A. WEST, J. M. AJELLO, M. H. STEVENS, D. F. STROBEL, G. R. GLADSTONE, J.S. EVANS, T. BRADLEY, TITAN AIRGLOW DURING ECLIPSE 19 June 2012R. West 1

TITAN’S ENERGETICS: SOLAR VS. MAGNETOSPHERIC “These Titan UV airglow observations are therefore comprised of emissions arising only from solar processes on N 2 with no detectable magnetospheric contribution.” Stevens et al., JGR 116, A05304, “…charged particle energy inputs can dominate all other energy input processes including solar UV.” Sittler et al., page 394, Chapter 16 in Titan from Cassini-Huygens, June 2012R. West2

MAGNETOSPHERIC ENERGY SOURCES: EVIDENCE FOR CHARGED PARTICLE PRECIPITATION - Solar XUV Excitation –Strong Top Ionosphere -Magnetospheric: p and O + Plasma Sporadic low ionosphere (Cravens et al., 2008). Kliore et al June 2012R. West3

IONIZATION RATES FROM THE T5 MEASUREMENTS Cravens et al., GRL June 2012R. West4

LAB SPECTRA e - ON N 2 MANGINA ET AL., June 2012R. West5

19 June 2012R. West6

UVIS ECLIPSE OBSERVATIONS Emissions are observed only during the DOY 127 event, the closest of the three. At that time the pixel scale was 660 km/pixel (not resolving the emitting region on the limb). 19 June 2012R. West7 From Ajello et al., 2012

UVIS OBSERVATIONS DAYSIDE FUV SPECTRA FROM STEVENS ET AL June 2012R. West8

UVIS OBSERVATIONS ECLIPSE FUV SPECTRA 19 June 2012R. West9

UVIS OBSERVATIONS DAYSIDE EUV SPECTRA FROM STEVENS ET AL June 2012R. West10

UVIS OBSERVATIONS ECLIPSE EUV SPECTRA 19 June 2012R. West11

HYDROGEN EMISSIONS 19 June 2012R. West12

CONCLUSIONS FOR THE UVIS ECLIPSE OBSERVATION EUV and FUV emissions from N and N 2 were observed at one of three eclipse events Only the strongest emission were observed, relative to what is seen from the illuminated atmosphere In the one event where emissions are observed the emitted intensities are about 0.1 times those seen on the dayside. The two events where no emissions were observed are more distant and therefore the non-detection may be a result of the smaller angle subtended by the emitting region. Examination of spectra at smaller distances would be a logical next step. About half of the 42.6±1.2 R of H Ly-αemission could be produced by reflection of the IPM Ly-α. The remainder is probably from proton recombination from precipitating protons 19 June 2012R. West13

ISS ECLIPSE OBSERVATIONS 19 June 2012R. West14

TWO VIEWS OF IMAGE W s EXPOSURE IN [CL1,CL2] Top panel: max I/F = 4X10-6; 40 km/pixel Bottom Panel: max I/F = 2X An image of Titan in sunlight but multiplied by 2X10 -5 was subtracted to remove scattered sunlight from Saturn’s limb. Inner circle at 300 km altitude; outer circle at 1000 km altitude. From West et al., manuscript submitted to GRL (2012) 19 June 2012R. West15

TWO VIEWS OF IMAGE W s EXPOSURE IN [CL1,CL2] Top panel: max I/F = 4X10-6 Bottom Panel: max I/F = 2X Inner circle at 300 km altitude; outer circle at 1000 km altitude. From West et al., manuscript submitted to GRL (2012) illuminated by sunlight from Saturn’s limb Deep airglow from within Titan’s haze Very faint glow between 300 and 1000 km 19 June 2012R. West16

SUMMARY ISS ECLIPSE OBSERVATIONS Three components are evident in the eclipse images Illumination by sunlight scattered and refracted around the limb of Saturn and (?) scattered from the rings. Attenuated from direct sunlight by 2X10 -5 An ‘ashen glow’ component is clearly evident on the anti-sun side of Titan. It appears as a uniform glow beyond the terminator. It may or may not have structure in the region where scattered sunlight was subtracted – hard to tell because subtracted residuals could be due to small differences in illumination and contrast on Titan A very faint limb glow between 300 and 1000 km altitude near the noise level. This is a very strange profile and not expected. Limb emission is homogeneous – no evidence for magnetic confinement. Interpretation of cloud-level contrasts is still open. 19 June 2012R. West17

SOURCE OF TITAN’S `ASHEN GLOW’ Lightning? No lightning has been detected by RPWS from any of the >70 Titan close flybys Illumination from Hyperion, Iapetus or Phoebe? Iapetus and Hyperion would produce a quarter moon or crescent appearance, not like the nearly uniform glow seen beyond the terminator Phoebe shine is too faint by about a factor of 10,000. Chemiluminescence? Maybe. HCNH + + e → CN+ H2 could yield ~13 R of near-UV to visible CN emissions (assuming a recombination rate of 2.8E-7(300/T) 0.65 and a yield of 33% for this path [Semaniak et al., 2001] Deeply penetrating cosmic rays produce N, N 2 emissions? Note: the deep ionosphere probed by radio occultation is also puzzling. Kliore et al proposed meteoritic impact. Still, the peak ionization is above 300 km. 19 June 2012R. West18

CASSINI UVIS OBSERVATIONS OF TITAN NIGHTGLOW SPECTRA 19 June 2012R. West19 Joseph M. Ajello, Robert A. West, Michael H. Stevens, Jacques Gustin, Kristopher Larsen, A. Ian F. Stewart, Larry W. Esposito, William E. McClintock, Gregory M. Holsclaw, E. Todd Bradley Submitted to JGR May, 2012

AJELLO ET AL., 2012 TITAN NIGHTSIDE EMISSIONS Analyzed 71 limb observations from 19 April, 2009 to 28 January, 2010 Obtained higher spatial resolution relative to the eclipse observations Obtained longer integrations and higher S/N than the eclipse observations 19 June 2012R. West20

19 June 2012R. West21 Geometric plots of each of the Titan limb and disk observations in 2009 by the EUV 1175 slit (2mR x 60 mR) demarking the EUV and FUV UVIS spectral observations. Eclipse Observation

CONCLUSIONS FROM AJELLO ET AL A number of emissions are seen that are difficult to see in the weaker eclipse spectrum (c4'(3,2) and c4'(4,3) bands at 945Å, the c4'(0,2) band at 1003 Å, the N I multiplet at 1134 Å and the N II 917 Å multiplet in the EUV) In the FUV we find the VK and LBH bands. The latter emission set particularly the VK system and the NI 1493 Å multiplet appears to be excited from below the 800 km limb ray height. 19 June 2012R. West22 Note: CH4 obscures emissions below about 800 km altitude

FROM CRAVENS ET AL., June 2012R. West23

SUPPLEMENTAL MATERIAL 19 June 2012R. West24

VOYAGER RESULTS FROM HALL ET AL., ESA SP 338, June 2012R. West25

UPDATE ON THE DETACHED HAZE 19 June 2012R. West26

TITAN, DIONE AND SATURN 2011 MAY June 2012R. West UV3 The haze is a single continuous layer across the S. pole

6 MAY, 2012 POLAR HOODS IN BOTH HEMISPHERES UV3 CB3 19 June 2012R. West28

MULTIPLE LAYERS SEEN IN UV3 6 MAY, June 2012R. West29

DETAIL AT 935 NM 6 MAY, June 2012R. West30