Interplanetary dust

The behavior of plasmas can be significantly altered when dust grains are present: such dust grains can become electrically charged, they have a large inertia so that they are less affected by the magnetic field, ...  This has a large impact on the types of waves that can be supported in a dusy plasma.

 

Wave phenomena in dusty plasmas

The study of dusty plasmas is a relatively new area of research in the field of plasma physics. Recent interest in such plasmas has increased because of observation of dust in the vicinity of comets and in laboratory devices, but much of the physics of dust in space is still unknown.

A dusty plasmas consists of dust grains (mainly micron sized) embedded in a tradional (e.g. electron-ion) plasma. The plasma particles will hit the dust grains, they become charged by different mechanisms (primary charging, photo-electron effects, secondary electron emission, field emission, ...) and are electromagnetically coupled to the plasma. Different examples are known in the solar system:

  • the rings of the major planets
  • asteroids
  • tails and comae of comets
  • the lower magnetosphere of the earth.

The grains are highly charged, 10.000 electron charges are typical, but their masses are even higher, of the order of 1.000.000 proton masses and higher.

One of the most striking features, explained by the physics of dusty plasmas are the spokes encountered in the B-ring of Saturn. These spokes (shown in the figure as grey radial structures in the dark background in the right lower corner of the photograph) are explained by dust grains that are levitated from large boulders in the ring plane.

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