Lecturer: Ingrid Mann (BIRA) Date: 2010-09-29 10:30 Place: Aniara
Nano Dust in the Solar Wind
Belgian Institute for Space Aeronomy (BIRA/IASB), Brussels, Belgium
The size distribution of solid objects in the interplanetary medium ranges from the km size of small solar system objects to smaller than micrometers. While dedicated dust instruments on spacecraft in most cases detect particles down to sizes of the order of 1/10 micrometer, recent measurements with the plasma wave instrument onboard STEREO point to the existence of smaller nanometric dust particles near 1AU (see Meyer-Vernet et al. Solar Physics 2009). The nano dust particles hit the spacecraft with velocities of the order of solar wind velocity and generate a small cloudlet of electrons and ions that cause the detected signal.
This presentation will address the formation of nano dust within the solar system dust cloud and the dynamics of nano dust in the solar wind that can lead to such high dust velocities. The majority of nano dust forms as collision fragments near the Sun, where it is either trapped at distances smaller than about 0.15 AU or ejected outward at larger distance. Trapping and ejection result from a combination of gravity, electric mirror and centrifugal force and depend on a number of different parameters. These dependencies possibly lead to time variation of the dust flux. Comparison of the nano dust to larger dust that forms in the inner solar and that is ejected by radiation pressure shows that the nano dust at 1 AU has distinctly different velocities than the larger dust.
The charge production due to nano dust impacting spacecraft also has to be considered for advanced particle and field measurements. Finally the transition region from nano dust to molecule and atom sizes is not observed yet, and the stability of dust in this size range is still an issue for future investigations.