Numerical Model of Formation of Ejecta Faculae on Ceres

On the dwarf planet Ceres, there are bright spots known as faculae. Four types of faculae are distinguished: (a) floor faculae, (b) faculae on Ahuna Mons, (c) rim/wall faculae found on craters' rims or walls, and (d) ejecta faculae in the form of bright ejecta blankets. Our investigation on the interaction of the hypothesized subsurface originated jet of gas and the granular material indicated that floor faculae (a) could be a result of separation of fine bright component of regolith. Here, we consider the hypothesis that the ejecta faculae (d) may be the result of separation of grains due to explosive gas expansion during the formation of the impact crater. We consider the axisymmetric gas motion above the surface of Ceres. We transform our system of equations into a dimensionless form. Our numerical model indicates that the separation effect is strong enough to separate the grains (according to size, density, and other aerodynamics properties). In some cases, separation gives a monotonic, systematic effect: smaller particles are ejected farther than heavier particles. Generally, however, the distance over which the particles will be thrown depends in a rather complicated way on the parameters of the particles and the parameters of motion of the gas. This property fits the faculae of type (d). Because we used the dimensionless form of the equations, our results can be also applied to other celestial bodies where the regolith contains volatile substances. This paper is an extension of our investigations on the origin of faculae (a).