Ejection velocities of dust particles from the near-surface layer of a cometary nucleus

Abstract Interpretation of observational data on dust environment, obtained in the vicinity of a cometary nucleus, requires realistic model of dust ejection from the surface. In the present paper we consider ejection of dust particles from a surface with cavities filled-up with products of sublimation. The goal of the work is to derive the method of assessment of the dust ejection velocity (i.e. particle’s velocity after acceleration in the jet from the cavity) as a function of the cavity volume and initial gas parameters in it. To this end the simulation of gas outflow accompanied by dust particle motion is carried out by the direct simulation Monte Carlo method. Dust particles of 5 mm and 5 cm size and cavities of different depth ratios were considered. The variation of particle velocity in an expanding jet was studied. For considering range of parameters it was found that: 1) the acceleration of ejected particles terminates at an altitude of about one particle radius; 2) the ejection velocity is less than 1.1 m/s; 3) only a small fraction (less than 2 per cent) of the cavity gas energy is transferred into kinetic energy of the dust particle, and this fraction decreases increasing the depth ratio. Based on the simulation results a simplified method for dust ejection velocity estimation is proposed. Assessments of ejection velocities for a wide range of pressures and gases (CO2, CO and H2O) were performed by the simplified method.