An Overview of the Asteroids and Meteorites

Abstract

The asteroids are a population of millions of small bodies found throughout the inner solar system but concentrated between Mars and Jupiter and ranging in size from hundreds of kilometers to meter-sized or smaller. Samples of asteroids are available in the form of meteorites, affording the opportunity for a unique synergy between geochemical and astronomical study. From laboratory and remote sensing studies, it is apparent that the asteroids harbor a range of compositions from metallic cores of once-molten bodies to primitive, ice-rich mixtures. This range of compositions is used to place constraints on the heating and cooling histories of asteroids. While igneous processes ceased on the asteroids very early on in solar system history, they have been heavily impacted since they formed. These impacts have generated regolith on asteroids of even small size, as well as formed craters, and in some cases entirely disrupted the target asteroids. As a result, most asteroids appear to be rubble piles, collections of material held together by little more than gravity and small-scale cohesive forces. Dynamical families are also created via impacts, with nongravitational forces affecting their orbits since their formation. The large number of asteroids, both in and out of families, has made them useful as test masses, allowing dynamicists to probe conditions early in solar system history, just as geochemists do with meteorites, and to model and constrain the motions of the larger planets. This chapter will provide a broad overview of asteroidal studies from the compositional to geophysical, from surfaces to cores.