| アブストラクト |
The activity of the Saturnian moon Enceladus was one of the biggest surprises of the ongoing Cassini-Huygens mission (Nasa/Esa) to Saturn. The icy satellite (500km diameter) exhibits an anomalously warm regions around its south pole. Connected to the thermal activity is an outflow of water gas from a prominent system of cracks in the ice crust. In the gas flow micron sized icy dust particles are entrained.
Gas and dust form a plume towering above the south pole which feeds the Saturnian magnetosphere with neutral gas and dust. Interestingly the ice grains show significant amounts of salts, pointing at a liquid origin. The Cosmic Dust Analyzer (CDA) onboard the CASSINI spacecraft obtained in-situ compositional measurements of freshly ejected particles in the Enceladus plume. A main result is that the proportion of salt rich particles is significantly enhanced in the plume, relative to the abundance inferred previously in the E ring. We show how this compositional profile in the plume, as well as the relative depletion in the E ring, arises as a consequence of a size-dependent dynamical filtering of particles. The generally larger size of salt rich grains (as compared to salt poor particles) leads to their enhanced concentration in the lower parts of the plume. From our model we infer the proportion of salt rich grains in the total flux of dust produced at Enceladus.
We find that the dominant part of the dust mass is salt rich. |
