Cratering of a comet nucleus by meteoroids

The two-dimensional axisymmetric hydrocode model of free particles is applied to the calculation of response of a comet nucleus to a meteorite impact. The nucleus is assumed to be spherical with a radius of 1 km. It is composed of a porous granular mixture of water ice and of mineral. Initial temperature is 50 K. Porosity is psi = 0.6 and the mean density is rho = 400 kg m(-3). Impactor radius is equal to 1 m and its mean density is equal to that of the nucleus. Impact velocity is 10 km s(-1). A normal impact is considered. Particular forms for the equations of state (EOS) for the real medium (water ice and rock) as well as for an artificial medium of very low-density (40 kg m(-3)) filling up the voids are used. The cohesion is included in the constitutive model of the constituents. Numerical modelling provides the time dependent fields of pressure, density, temperature, and particle velocity in the vicinity of an impact point. The evolution of the field of temperature correlated with the function for kinetics of amorphous to crystalline phase transition permits discussion of the impact-induced crystallization of presumably initially amorphous ice. (C) 1999 COSPAR. Published by Elsevier Science Ltd.