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Molecular Physics seminar

Titan and Enceladus Composition measured with Cassini INMS and CAPS: Implications for the formation and evolution of the Saturn system

by J. Hunter Waite (South West Research Institute, USA)

FA31 ()


The Cassini Ion Neutral Mass Spectrometer (Cassini INMS) continues to return a wealth of information about the Saturn satellites, Titan and Enceladus. Earlier data from Titan indicated an unanticipated organic complexity in the upper atmosphere. Ion-neutral chemistry plays a key role in the reaction mechanisms that lead to this organic complexity as evidenced by the abundance of high molecular weight positive and negative ions observed by the Cassini Plasma Spectrometer (CAPS). Recent results from Enceladus also indicate an unanticipated organic complexity in the plume gases emanating from the interior that is quite different from that at Titan. The organic composition indicates both primordial organics similar to those seen in comets, as well as olefins that may be the result of Fischer-Tropsch (F-T) reactions in the interior. The existence of F-T chemistry is consistent with the measureable presence of 40Ar and ammonia and is further evidence of a liquid interior. A D/H ratio from water vapor that is similar to the long period comets Halley and Hale-Bopp speaks to the origin and formation of icy bodies in the outer solar system. The measured ratio of D/H of 3 x 10-4 is consistent with the recent Composite Infrared Spectrometer (CIRS) measurements of D/H in methane at Titan suggesting a similar origin for the materials that make up these two Saturn moons. Compositional measurements from both moons suggest an icy origin in the outer solar system followed by a partial devolatization in the Saturn nebula with loss of N2 and CO, but retention of primordial CH4 as recently reported in separate papers by Mousis et al. and Glein et al. in Icarus (see online papers).