Spontaneous formation of nonspherical water ice grains in a plasma environment
Saturn's rings, terrestrial polar mesospheric clouds, and astrophysical molecular clouds are all dusty plasma environments where tiny grains of water ice are an important constituent. Existing models typically assume that the ice grains are spherical and then invoke various arguments about the normal distribution or the power law dependence of grain number density on grain radius. Using a laboratory plasma in which water ice grains spontaneously form, we investigated the validity of the traditional assumption that these grains are spherical. We found that in certain cases at low ambient pressures, water ice grains in the laboratory dusty plasma are not spherical but instead are highly elongated, i.e., ellipsoidal. Preliminary analysis suggests that electrical forces associated with the dusty plasma environment are responsible for the nonspherical shape.
© 2013 American Geophysical Union. Received 8 October 2013; revised 4 November 2013; accepted 6 November 2013; published 3 December 2013. This work was supported by the USDOE/NSF Partnership in Plasma Science. We thank S. Shimizu for graciously providing detailed information on the experimental setup used in Shimizu et al. . The Editor thanks an anonymous reviewer and Mihaly Horanyi for their assistance evaluating this manuscript.
Published - grl51127.pdf