Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p23c..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P23C-07
Physics
[1060] Geochemistry / Planetary Geochemistry, [6213] Planetary Sciences: Solar System Objects / Dust, [6265] Planetary Sciences: Solar System Objects / Planetary Rings, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites
Scientific paper
After E ring ice grains, Saturnian stream particles are the second most abundant dust species encountered by the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. They are nanometer-sized dust particles ejected from Saturn’s magnetosphere with speed higher than 100km/s. In this work we analyse the dynamics and composition of Saturnian stream particles based on measurements during 2004 and 2005 with unexpected implications for aqueous processes on Enceladus. From backward tracing the most likely source of stream particles is Saturn's E ring. In contrast to E ring particles whose composition is dominated by water ice an updated analysis of CDA mass spectra confirms that silicates are the most abundant compounds of Saturnian stream particles. This compositional discrepancy can be modelled and explained by a dynamical simulation which takes into account the erosion efficiencies of the material. We find that Saturnian stream particles are likely sputter-resistant, nano--silica raisins released from the water ice matrix of micron-sized E ring grains by plasma sputter erosion. Since Enceladus is the main source of these grains, they in turn serve as a probe to study the interior of the enigmatic icy moon. It is remarkable that the silicates identified in stream particles are poor in metals. The composition is not in agreement with the composition expected from interplanetary dust (like olivine or pyroxene) and in most cases seems to be dominated by silica (SiO2). The formation of nano—silica requires an aqueous phase. On Earth their formation is an ubiquitous process and has been applied in industry and geochemistry. A water reservoir in contact with any rocky material transforms dissolved SiO2 into nanocolloid with a reaction rate depending on the physical and chemical conditions of the solution. This finding is an independent indication of water-rock interaction on Enceladus and provides constraints, such as ionic strength and pH value.
Hsu Haoran
Kempf Sascha
Postberg Frank
Trieloff Mario
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