An experimental view on the collisional properties of cm-sized Saturnian ring particles
Abstract
Saturn's dense main rings are composed of 1-cm- to 10-m-sized almost pure water ice particles. Their dynamics is dominated by two competing effects. On one hand, gravitational perturbations of the particles' motion by the planet itself or its nearby moons increase the orbital eccentricity and, thereby, spread the vertical thickness of the rings. On the other hand, frequent dissipative collisions among the ring constituents at very low relative velocities (less than ∼ 1 cm s-1) cause the re-circularization of their orbits and confine the ring thickness to less than ∼ 5 m.
Unlike the numerous observational data obtained by spaceborne and ground-based methods, only very limited laboratory measurements exist on the collision properties of icy particles at velocities relevant for Saturn's main rings. Up to now, experiments have predominantly been restricted to quasi-two-dimensional collisions of large icy spheres or to impacts at significantly higher velocities. We have recently performed experimental investigations on collisions at velocities between 10 cm s-1 and 1.5 mm s-1 among solid ice samples within a freely colliding ensemble of 10-mm-sized ice spheres. Additionally we gained data on the collisions between similar samples covered with a layer of micrometer-sized SiO2 grains, representing a loose regolith layer. These experiments were performed in the microgravity environment of the Bremen drop-tower facility, so that particle impacts could be studied in three dimensions and with arbitrary impact parameters. We will present the results obtained for the coefficient of restitution as a measure of the energy loss in low-velocity binary collisions of icy spheres. Furthermore, we will report on sticking collisions between cm-sized solid ice spheres observed in our many-body experiments.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.P13B1670H
- Keywords:
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- 5759 PLANETARY SCIENCES: FLUID PLANETS / Rings and dust;
- 6020 PLANETARY SCIENCES: COMETS AND SMALL BODIES / Ices;
- 6045 PLANETARY SCIENCES: COMETS AND SMALL BODIES / Physics and chemistry of materials;
- 6265 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS / Planetary rings