Motion of Cometary Dust

On timescales of days to months, the motion of cometary dust is mainly affected by solar radiation pressure, which determines dust dynamics according to the particle-scattering crosssection. Within this scenario, the motion of the dust creates structures referred to as dust tails. Tail photometry, depending on the dust cross-section, allows us to infer from model runs the best available outputs to describe fundamental dust parameters: mass loss rate, ejection velocity from the coma, and size distribution. Only models that incorporate these parameters, each strictly linked to all the others, can provide self-consistent estimates for each of them. After many applications of available tail models, we must conclude that comets release dust with mass dominated by the largest ejected boulders. Moreover, an unexpected prediction can be made: The coma brightness may be dominated by light scattered by meter-sized boulders. This prediction, if confirmed by future observations, will require substantial revisions of most of the dust coma models in use today, all of which are based on the common assumption that coma light comes from grains with sizes close to the observation wavelength.