Structure, composition, and origin of meteoroids

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Comets and asteroids are relatively unchanged since the formation of the solar system. Unlike the planets, which have melted and differentiated, comets and primitive asteroids contain the basic grains which were present before the planets were formed. Comets in particular are very difficult to study directly, because they are moving very quickly as they approach the Earth, making it difficult for spacecraft to visit them. Samples have been returned from just one comet, Wild 2, by the Stardust mission. The tiny grains sampled by that spacecraft include solid, rocky grains that formed at high temperature: how such solid grains, which must have formed close to the sun in the hottest and densest part of the nebula, were incorporated into icy comets, which obviously formed far from the sun, is a mystery. Meteoroids are small objects which have been separated from comet and asteroid parent bodies, and they strike the Earth in large numbers every day. We will use a new, high-resolution observing system to work out the fine structure and composition of meteoroids from three different populations: asteroids, comets which formed among the giant planets, and comets which formed beyond Neptune's orbit. The new system allows us to watch how meteoroids break up as they collide with the Earth's atmosphere, which will allow us to tell if they are strong, solid particles or weak clusters of dust. A spectral system will give us clues about the mineral composition of the individual grains. In particular, we will search for the sort of solid particles commonly found in asteroids. Knowing whether these solid grains are present in each population, and how common they are, will help to choose among many models of the early solar system, and help us to understand the formation of the planets.