The influence of hemispherical albedo on the dynamics of cometary particles

Abstract

This paper presents a new approach to determining the dimensions of particles that can be lifted to a coma by the sublimation flux of water ice. Due to the diverse colour of the cometary surfaces, in the presented calculations we take into account the influence of the reflectance coefficient (hemispherical albedo) on the size of particles lifted from the surface of the nucleus. A Cary 5000 spectrometer was used to measure hemispherical albedo. Spectroscopic measurements used dust particles that consisted of pure silicate or were a mixture of pure silicate and organic compounds such as charcoal, soot, and ash. In addition, these admixtures acted as a means of darkening the tested sample. Depending on the colour of the sample and the wavelength, the measured value of hemispherical albedo oscillated in the range from 4.93 per cent to 48.65 per cent. A thermodynamic model of cometary matter emission was developed based on the results of hemispherical albedo measurements. The performed numerical simulations show that the temperature decreases with the increase of the hemispherical albedo, which translates into the sublimation flux and the dynamics of the dust-ice particles present on the surface of the cometary nucleus. Taking into account the extreme values of the hemispherical albedo, the differences in the size of particles carried away from the surface of the nucleus are in the order of centimeters.