9 - Asteroid impact

Summary

Introduction

Matter in the universe exists in a series of states; three that are well known from standard experience, solid, liquid and gas, and the plasma state in which gas is ionised. Other more esoteric states are possible but the four above occupy the main thrust of this book. This volume has confined itself to pressures in the range up to a megabar and temperatures below 10000 K in which solids exhibit strength that is based upon the interaction of valence electrons. Beyond a critical energy density bonding is determined by further interactions of inner orbital electrons and concepts from the ambient cannot be extended.

Equally the forces acting on matter applicable to this work are electrostatic or gravitational. Electrostatic forces may act over great distance but as length scale increases there is sufficient matter that substances behave as neutral. The long-range attractions at the microscale are due to Van de Waals’ forces that might operate over distances of the order of 10 nm between polymer chains and are important in binding matter at the mesoscale. Components on a scale of centimetres are naturally held under gravity in stacks or compressed under lateral forces by some restraint. The strength of such an interface in tension is determined by that of the pin or joint that constrains the interface between the two components. At this scale, flow occurs by hinging around pivots under load or by slip along the fracture line with frictional heating at the interface. At the planetary scale forces are gravitational and slip occurs down faults that allow flow under shear.