Contributed Talk

Nanodust in the Interstellar Medium: Comparison to Observations in the Solar System

¹Ingrid Mann, ²Aigen Li (¹EISCAT Scientific Association and Umea University, Sweden, ²Department of Physics and Astronomy, University of Missouri, USA)

Many of the unexplained spectral phenomena in the interstellar medium (ISM) are hypothesized to be associated with the presence of nanodust. Nanodust is typically used to ascribe solid particles of sizes smaller than several 10 nm, though one may also denote as nanodust in the ISM those solid particles that are subject to stochastic heating. Nanodust is also recently observed in the solar system and in this presentation we compare findings from solar system observations to conditions in the ISM.

While dust particles form the ISM continuously flow into the solar system, the grains with sizes smaller than 5 nm are deflected by the magnetic field that builds up in the outer solar system due to interaction of the local ionized ISM gas with the solar wind. Nanodust in the solar system forms locally within the interplanetary dust cloud or from solar system objects. Nanodust is observed due to several different physical processes, like UV light-scattering, stochastic heating, electric dipole radiation of rotating nanodust, photoluminescence, and photoelectric heating of the surrounding gas, to name those that are most important in the ISM. We show that observing solar system nanodust by these processes is less likely and we describe some of the observations of nanodust by in-situ measurements from spacecraft.

Interpretation of the in-situ measurements suggests that mutual dust collisions can generate nanodust as small as a few nm by fragmentation. The in-situ measurements further suggest that nanodust has significantly higher velocities than would be expected from Keplerian motion and this results from interaction of the charged dust with the solar wind. The dynamics of nanodust in the solar wind exemplifies efficient dust acceleration in a cosmic plasma. We finally show that active radar experiments in the upper Earth atmosphere may even be used to study the process of dust charging.

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