1 - Introduction

Summary

Solar System history started some 4567 million years ago with the collapse of an interstellar molecular cloud to a protoplanetary disk (the solar nebula) surrounding a central star (the Sun). Evolution of the Solar System continued through a complex process of accretion, coagulation, agglomeration, melting, differentiation and solidification, followed by bombardment, collision, break-up, brecciation and re-formation, then to varying extents by heating, metamorphism, aqueous alteration and impact shock. One of the key goals of planetary science is to understand the primary materials from which the Solar System formed, and how they have been modified as the Solar System evolved. The last two decades have seen a greater understanding of the processes that led to the formation of the Sun and Solar System. Advances have resulted from astronomical observations of star-formation regions in molecular clouds, the recognition and observation of protoplanetary disks and planetary systems around other stars, and also from advances in laboratory instrumentation that have led to more precise measurements on specific components within meteorites, e.g., refinement of chronologies based on shortlived radionuclides. Results from meteorites are important because meteorites are the only physical materials available on Earth that give direct access to the dust from which the Solar System formed. Study of meteorites allows a more complete understanding of the processes experienced by the material that resulted in the Earth of today.

Naming of meteorites

Meteorites are pieces of rock and metal, almost all of which are fragments broken from asteroids during collisions. They fall at random over the Earth's surface, and have also been identified as components within lunar soils [1.1, 1.2] and on Mars’ surface [1.3]. Meteorites are named from their place of find or fall, traditionally after a local geographic feature or centre of population. However, where large numbers of meteorites are found within a limited area, this convention is not possible to follow. The recovery of meteorites from desert regions has resulted in a name–number nomenclature that combines geographic and date information. Antarctic specimens collected by government-funded expeditions are given a year–number combination with a prefix recording the icefield from which they were retrieved (e.g., Allan Hills 84001), whereas meteorites collected in hot deserts are simply numbered incrementally by region (e.g., Dar al Gani 262).