Composition of Titan's ionosphere

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Editor's Highlight Read Full Article (file size: 491329 bytes) Cited by GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L07105, doi:10.1029/2005GL025575, 2006 Composition of Titan's ionosphere T. E. Cravens Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, USA I. P. Robertson Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, USA J. H. Waite Jr. Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA R. V. Yelle Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA W. T. Kasprzak NASA Goddard Space Flight Center, Greenbelt, Maryland, USA C. N. Keller Division of Science, Math, and Kinesiology, Cornerstone University, Grand Rapids, Michigan, USA S. A. Ledvina Space Sciences Laboratory, University of California, Berkeley, California, USA H. B. Niemann NASA Goddard Space Flight Center, Greenbelt, Maryland, USA J. G. Luhmann Space Sciences Laboratory, University of California, Berkeley, California, USA R. L. McNutt Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA W.-H. Ip Institutes of Astronomy and Space Science, National Central University, Chung-Li, Taiwan V. De La Haye Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA I. Mueller-Wodarg Space and Atmospheric Physics Group, Imperial College, London, UK J.-E. Wahlund Swedish Institute of Space Physics, Uppsala, Sweden V. G. Anicich NASA Jet Propulsion Lab, Pasadena, California, USA V. Vuitton Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA Abstract We present Cassini Ion and Neutral Mass Spectrometer (INMS) measurements of ion densities on the nightside of Titan from April 16, 2005, and show that a substantial ionosphere exists on the nightside and that complex ion chemistry is operating there. The total ionospheric densities measured both by the INMS and the Cassini Radio and Plasma Wave (RPWS) experiments on Cassini suggest that precipitation from the magnetosphere into the atmosphere of electrons with energies ranging from 25 eV up to about 2 keV is taking place. The absence of ionospheric composition measurements has been a major obstacle to understanding the ionosphere. Seven “families” of ion species, separated in mass-to-charge ratio by 12 Daltons (i.e., the mass of carbon), were observed and establish the importance of hydrocarbon and nitrile chains in the upper atmosphere. Several of the ion species measured by the INMS were predicted by models (e.g., HCNH⁺ and C₂H₅ ⁺). But the INMS also saw high densities at mass numbers not predicted by models, including mass 18, which we suggest will be ammonium ions (NH₄ ⁺) produced by reaction of other ion species with neutral ammonia. Received 16 December 2005; accepted 3 March 2006; published 11 April 2006. Index Terms: 5435 Planetary Sciences: Solid Surface Planets: Ionospheres (2459); 2419 Ionosphere: Ion chemistry and composition (0335); 2431 Ionosphere: Ionosphere/magnetosphere interactions (2736); 2455 Ionosphere: Particle precipitation; 6281 Planetary Sciences: Solar System Objects: Titan. Read Full Article (file size: 491329 bytes) Cited by Citation: Cravens, T. E., et al. (2006), Composition of Titan's ionosphere, Geophys. Res. Lett., 33, L07105, doi:10.1029/2005GL025575. Copyright 2006 by the American Geophysical Union.

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