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  • 1
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    No sodium in the vapour plumes of Enceladus (2009)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2009-06-26
    Description: The discovery of water vapour and ice particles erupting from Saturn's moon Enceladus fuelled speculation that an internal ocean was the source. Alternatively, the source might be ice warmed, melted or crushed by tectonic motions. Sodium chloride (that is, salt) is expected to be present in a long-lived ocean in contact with a rocky core. Here we report a ground-based spectroscopic search for atomic sodium near Enceladus that places an upper limit on the mixing ratio in the vapour plumes orders of magnitude below the expected ocean salinity. The low sodium content of escaping vapour, together with the small fraction of salt-bearing particles, argues against a situation in which a near-surface geyser is fuelled by a salty ocean through cracks in the crust. The lack of observable sodium in the vapour is consistent with a wide variety of alternative eruption sources, including a deep ocean, a freshwater reservoir, or ice. The existing data may be insufficient to distinguish between these hypotheses.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schneider, Nicholas M -- Burger, Matthew H -- Schaller, Emily L -- Brown, Michael E -- Johnson, Robert E -- Kargel, Jeffrey S -- Dougherty, Michele K -- Achilleos, Nicholas A -- England -- Nature. 2009 Jun 25;459(7250):1102-4. doi: 10.1038/nature08070.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory for Atmospheric & Space Physics, University of Colorado, Boulder, Colorado 80309, USA. nick.schneider@lasp.colorado.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19553993" target="_blank"〉PubMed〈/a〉
    Keywords: Exobiology ; Gases/*chemistry ; *Moon ; Planets ; Sodium/*analysis ; Spectrum Analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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    PAPER CURRENT
  • 2
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    Ion Temperature Control of the Io Plasma Torus (2005)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: We report on observational and theoretical studies of ion temperature in the Io plasma torus. Ion temperature is a critical factor for two reasons. First, ions are a major supplier of energy to the torus electrons which power the intense EUV emissions. Second, ion temperature determines the vertical extent of plasma along field lines. Higher temperatures spread plasma out, lowers the density and slows reaction rates. The combined effects can play a controlling role in torus energetics and chemistry. An unexpected tool for the study of ion temperature is the longitudinal structure in the plasma torus which often manifests itself as periodic brightness variations. Opposite sides of the torus (especially magnetic longitudes 20 and 200 degrees) have been observed on numerous occasions to have dramatically different brightness, density, composition, ionization state, electron temperature and ion temperature. These asymmetries must ultimately be driven by different energy flows on the opposite sides, presenting an opportunity to observe key torus processes operating under different conditions. The most comprehensive dataset for the study of longitudinal variations was obtained by the Cassini UVIS instrument during its Jupiter flyby. Steffl (Ph.D. thesis, 2005) identified longitudinal variations in all the quantities listed above wit the exception of ion temperature. We extend his work by undertaking the first search for such variation in the UVIS dataset. We also report on a 'square centimeter' model of the torus which extend the traditional 'cubic centimeter' models by including the controlling effects of ion temperature more completely.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Poster 60.13
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    NASA TECHNICAL REPORTS
  • 3
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    On the Origin of System III Asymmetries in the Io Torus (2006)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: The Io plasma torus exhibits several intriguing asymmetries which offer insights to the processes that transport mass and energy through the system. While these asymmetries are increasingly well described observationally, most still lack physical explanations. One important asymmetry is fixed in the coordinate system corotating with Jupiter's magnetic field. Space-based and ground-based observations have shown that torus ions are hotter and more highly ionized around System III 20 deg. Our simulations show that this type of torus asymmetry can be caused by enhanced pickup of fresh ions from Io's neutral clouds near these longitudes. The enhancement is caused primarily by the tilt and offset of the torus relative to the neutral clouds. We will report on the model parameters required to match the observed asymmetries, and offer predictions which will allow a test of this hypothesis.
    Keywords: Lunar and Planetary Science and Exploration
    Format: text
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    NASA TECHNICAL REPORTS
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