Jan-Martin Hertzsch
Brunel University, Department of Mathematical Sciences,
Uxbridge, UB8 3PH, United Kingdom
masrjmh@brunel.ac.uk
An important problem in planetary science and meteoritics is the growth of medium-sized bodies from small ice and dust grains. It is also an interesting example of structure formation in granular systems. Surface properties of the grains play a crucial role in this process since they affect their collisional properties.
In order to understand the behaviour of grains during a collision, a theoretical model has been developed which describes the change in the normal and tangential relative velocity of two colliding particles, generalizing earlier approaches by taking into account combined effects of different nature. It is based on an analysis of the elastic, viscous, and friction forces acting in the material and on the surfaces including adhesion due to molecular forces between the bodies in contact. In particular, the latter can lead to aggregation.
From the equations of motion, the restitution coefficients are calculated for normal and tangential relative velocity in dependence on the initial velocity for various sets of parameters such as elasticity, viscosity, surface roughness, and adhesive strength, which correspond to different materials. Special attention is given to water ice which is a major constituent of the material in comets and in planetary rings.
The relationship between restitution coefficients and impact velocity obtained from the model will be useful in numerical many-particle simulations of aggregation processes in the solar system.