Statistical Description of Granular and Dust Populations

Details Statistical Description of Granular and Dust Populations Statistical Description of Granular and Dust Populations

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....10760s&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10760

Physics

Scientific paper

Although physical collisions are rare in cosmic dust ensembles they may play an important role in some cases, e.g. for the formation of planetesimals from dust, or for sources (of beta meteoroids) and sinks of dust (possibly self-sustained E ring of Saturn) caused by fragmenting collisions. In this context statistical equations are derived describing the evolution in a phase space built up by space coordinates, velocities and masses. Three cases: i) coagulation, ii) restitution, and iii) fragmentation are discussed and it is emphasized that the collision dynamics decides, which of these cases occurs. In the coagulation regime the Smoluchowski equation is obtained if and only if a Maxwellian velocity distribution, equal ``granular'' temperatures, and particle sticking at any contact are assumed. These assumptions can not be hold in many cases. For example, it is hard to assume dust populations to be in ``thermal'' equilibrium, because of their sensitivity to a wealth of perturbations and due to low collision frequencies. Additionally, fragmentation and restitution will occur if the impact speed exceeds a threshold. We derived a coagulation equation considering such a threshold speed. Furthermore, we unify all three regimes (coagulation, restitution, fragmentation) in a generalized kinetic concept. The usefulness of our unified description is demonstrated for several dust populations.

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