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  • 1
    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
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  • 2
    Publication Date: 1989-12-15
    Description: Results from the occultation of the sun by Neptune imply a temperature of 750 +/- 150 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane, acetylene, and ethane at lower levels. The ultraviolet spectrum of the sunlit atmosphere of Neptune resembles the spectra of the Jupiter, Saturn, and Uranus atmospheres in that it is dominated by the emissions of H Lyman alpha (340 +/- 20 rayleighs) and molecular hydrogen. The extreme ultraviolet emissions in the range from 800 to 1100 angstroms at the four planets visited by Voyager scale approximately as the inverse square of their heliocentric distances. Weak auroral emissions have been tentatively identified on the night side of Neptune. Airglow and occultation observations of Triton's atmosphere show that it is composed mainly of molecular nitrogen, with a trace of methane near the surface. The temperature of Triton's upper atmosphere is 95 +/- 5 kelvins, and the surface pressure is roughly 14 microbars.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Broadfoot, A L -- Atreya, S K -- Bertaux, J L -- Blamont, J E -- Dessler, A J -- Donahue, T M -- Forrester, W T -- Hall, D T -- Herbert, F -- Holberg, J B -- Hunter, D M -- Krasnopolsky, V A -- Linick, S -- Lunine, J I -- McConnell, J C -- Moos, H W -- Sandel, B R -- Schneider, N M -- Shemansky, D E -- Smith, G R -- Strobel, D F -- Yelle, R V -- New York, N.Y. -- Science. 1989 Dec 15;246(4936):1459-66.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17756000" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 1987-10-02
    Description: The satellites of Jupiter eclipsed each other in 1985, and these events allowed an unusual measurement of the sodium in Io's extended atmosphere. Europa was used as a mirror to look back through the Io atmosphere at the sun. The measured column abundances suggest that the atmosphere is collisionally thin above 700 kilometers and may be collisionally thin to the surface. The sodium radial profile above 700 kilometers resembles a 1500 kelvin exosphere with a surface density near 2 x 10(4) sodium atoms per cubic centimeter, but a complete explanation of the dynamics requires a more complex nonthermal model: the calculated loss rates suggest that the atmosphere is being replaced on a time scale of hours.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schneider, N M -- Hunten, D M -- Wells, W K -- Trafton, L M -- New York, N.Y. -- Science. 1987 Oct 2;238(4823):55-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17835653" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    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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  • 5
    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
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  • 6
    Publication Date: 1989-12-15
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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