1. Titan Glows in the Dark – West et al. and Ajello et al., 2012 R. A.. West, J. M. Ajello, M. H. Stevens, D. F. Strobel, G. R. Gladstone, J. S. Evans, and E. T. Bradley, Titan airglow during eclipse, Geophys. Res. Lett. 39, L18204, doi:10.1029/2012GL053230, 2012 J. M. Ajello, R. A. West, J. Gustin, K. Larsen, A. I. F. Stewart, L. W. Esposito, W. E. McClintock, G. M. Holsclaw, and E. T. Bradley, Cassini UVIS observations of Titan nightglow spectra, J. Geophys. Res. Space Physics, 117, A12, doi:10.1029/2012JA017888, 2012

2. Geometry of the eclipse observation

3. Dayglow. From Stevens et al., 2011 EUV FUV

4. Eclipse Spectra EUV FUV Result: Darkside airglow intensity is about 10% of dayside airglow. Insufficient spatial resolution to determine altitude profile of the emission.

5. Primary Conclusion from UVIS Spectra: Emissions from charged particle precipitation contribute about 10% of the power from peak solar-stimulated emissions

6. Visible wavelengths Sunlight at 2X 10- 5 of direct illumination Airglow 300-1000 km altitude Airglow at or below 300 km altitude (within the haze or scattered external radiation. From cosmic rays? If so, it implies that cosmic ray-generated airglow is much stronger than H +, O + the magnetosphere!!!! Chemiluminescence, eg HCNH + + e -> CN + H 2 with CN excited producing photons? More work on these ideas is needed. In the bottom panel the reflected sunlight has been subtracted, more or less Good spatial resolution, poor spectral resolution. New questions to ponder

7. Ajello et al. study Observations from19 April 2009 through 28 January 2010 Most have higher spatial resolution than the eclipse observations, but still, vertical profiling is difficult.

8. Summary Beyond 120 solar zenith angle, when the upper atmosphere of the moon is in total darkness, there are UV emissions from plasma impact of charged particles [Cravens et al., 2008] over an extended altitude from 500 to 1200 km. The weak emissions are variable and occur at about 10– 20% of the level of the dayglow.