Heidelberg Dust Research Group
Heidelberg Dust Research Group
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Latest News |
| Cassini traverses a plume on Saturn's icy moon Enceladus |
| On July 14th 2005 the Cassini spacecraft had an encounter with the Saturnian moon Enceladus at a distance of 175km - well inside the moon's sphere of gravitational influence. This allowed the direct measurement of the distribution of the freshly produced dust at the source of Saturn's E ring. The data indicated that a significant part of the dust particles is possibly produced by an ice sources on the south polar region of the moon. Dust grains slower than the escape velocity form a cloud around the satellite, whereas the faster grains replenish Saturn's E ring. These measurements were done by the High Rate Detector (HRD) (designed and build by the University of Chicago) which is part of the Cosmic Dust Analyser (CDA) instrument on Cassini operated by scientists at the Max-Planck-Institute of Nuclear Physics in Heidelberg, Germany. Design and preliminary analysis of the measurements is based on models which were developed in the University of Potsdam, Germany. |
 This picture shows the icy moon Enceladus. The "Tiger Stripes", favoured to be the main sorce of the E ring, are in the right bottom of the picture, around the south pole of the moon. image: NASA/JPL |
| Saturn's remarkable E ring is the largest ring of our solar system. Based on optical measurements it is surprisingly found to mainly consist of ice particles of approximately the same size (radii between 0.3 and 2 microns), though the source of the ring, the icy moon Enceladus, feeds the ring with grains having a much broader mass distribution. Because of this contradiction, the mass distribution of the ring must be closely connected to the dynamics of the ring particles which is yet to be clearly understood. A direct measurement of the ice particles close to Enceladus promises a better understanding of the complex nature of the E ring. |
 View of Saturn's E ring as seen in the ultraviolet by the Hubble Space Telescope's Wide Field and Planetary Camera during the 1995 ring plane crossing. Saturn's main rings are overexposed near the bottom edge. The E ring peaks in brightness at around the orbit of Enceladus at 3.9 Saturn radii. Image: Phil Nicholson (Cornell), Mark Showalter (NASA-Ames/Stanford) and NASA |
| Profitable for the analysis of the Cassini data is the fact that the HRD sensor is able to detect only particles which are greater than the typical E Ring particles. Until recently it was assumed that the dust at Enceladus is produced similar to the dust at the Galilean moons of Jupiter: fast dust grains striking the moon's surface generating ejecta particles. However, preliminary analysis of data indicated that the majority of the Enceladus grains must have originated from a source at the moon's south pole which was found to be significantly warmer than expected. Probably the best interpretation of these findings is that the increased activities in this area jettisons the grains and they reach outside, beyond Enceladus' sphere of gravitational influence. |
| see also: german press release of the Max-Planck-Gesellschaft |
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