INMS quarterly report: Aug.-Sept., 2005 Science highlights –In situ determination of the atmosphere of Enceladus much beyond anticipation - water 90%, carbon monoxide or molecular nitrogen 4%, carbon dioxide 3%, and methane 1-2%. –Plume structure indicates two sources of outgassing: one global and one associated with venting from the hotspot.

Enceladus Atmosphere As Viewed From INMS View of Enceladus showing surface features and the Cassini ground track during the flyby on July 14, The south polar hot spot is shown in red, amidst the surface feature known as the ‘Tiger stripes’. The spacecraft trajectory is shown in yellow. The color of the points along the trajectory represent: purple, Cassini’s closest approach to Enceladus; red, the closest approach to the ‘south polar hot spot’; black, the point along the track where INMS saw the maximum in water vapor density; green, the point along the track where the Cassini Cosmic Dust Analyzer (CDA) saw the peak in dust particle density.

Enceladus Atmosphere As Viewed From INMS H 2 O: 91% CO 2 : 3% N 2 or CO: 3-4% CH 4 : 1-2% The average mass spectrum for altitudes below 500 km. The solid black line indicates the measured average spectrum and the red symbols represent the reconstructed spectrum. The error bars displayed are the larger of the 20% calibration uncertainty or the one-sigma statistical uncertainty. The dissociative ionization products produced by the electron ionization source for each constituent are shown above the figure.

INMS quarterly report: Aug.-Sept., 2005 Science plans –Upcoming INMS measurements of Titan’s atmosphere on T8 will continue to investigate the variability of Titan’s atmosphere in hopes of setting more definitive guidelines for the safe altitude of future Titan flybys. –Excellent INMS measurements of the atmosphere from the recent flyby of Enceladus suggest that a close flyby (~25 km) planned for orbit 061 with INMS in the ram direction will allow a definitive determination of the atmospheric composition including a measurement of the D/H and 14 N/ 15 N ratios.

INMS quarterly report: Aug.-Sept., 2005 Talks given by the INMS team 1. Mueller-Wodarg, I. C. F, R. V. Yelle, N. Borggren, and J. H. Waite, Waves and Horizontal Structures in Titan's Thermosphere, Poster at the 37th Annual Meeting of the Division of Planetary Sciences of the American Astronomical Society in Cambridge, UK, Sept 04-09, T. E. Cravens, I. P. Robertson, J.-E. Wahlund, J. H. Waite Jr., S. A. Ledvina, H. B. Niemann, R. V. Yelle, W. T. Kasprzak, J. G. Luhmann, R. L. McNutt, W.-H. Ip, V. De La Haye, I. Müller-Wodarg, D. T. Young, A. J. Coates, Y. Ma, A. F. Nagy, C. N. Keller, Titan‚s Ionosphere: Model Comparisons with Cassini Data, Talk at the Magnetospheres of Outer Planets meeting in the UK, August 2005.

INMS papers: Aug.-Sept., Waite, Jr., J. Hunter, et al., Ion Neutral Mass Spectrometer (INMS) results from the first flyby of Titan, Science, 308, , Waite, J. H., Jr., et al., The atmospheric plume of Enceladus as observed by the Cassini Ion Neutral Mass Spectrometer, Science, submitted, Yelle et al.,Titan atmospheric structure submitted to JGR in June, Cravens, T. E., et al., "Titan's ionosphere: Model comparisons with Cassini Ta data," Geophys. Res. Letts. 32, doi: /2005GL023249, Ip, W.-H., An update on the ring exosphere and plasma disc of Saturn, GeoRL, /2004GL022217, De La Haye et al., Titan atmospheric composition in preparation for JGR, Cravens et al., Titan ionospheric composition in preparation for JGR, Luhmann et al., The ring ionosphere in preparation for Icarus, Mueller-Wodarg, I. C. F., R. V. Yelle, N. Borggren, and J. H. Waite, Waves and horizontal structures in Titan’s thermosphere, to be submitted to Icarus, 2005.