We think that some of it clumps together to form comets and other smaller bodies, which eventually collide to build up the planetary sized bodies. The dust that does not get entombed in small bodies, will eventually be blown out of the solar system by the Sun during its 'T-Tauri Wind' phase, or by solar radiation pressure.
We can actually collect these ancient dust grains from certain types of meteorites, and see them as distinct geologic inclusions that can be harvested for independent study and chemical analysis. From the isotopic abundances of these grains, astronomers have been able to explore the origin of these dust grains in very ancient red giant stars which produced them in their outer, cool atmospheres. The dust grains essentially condense like rain drops and are ejected by the star into interstellar space over 100 million years before they arrived in the cloud that produced our own solar system. NASA's Genesis mission plans to capture interplanetary and interstellar dust grains and return them to earth for direct study.
For more about interplanetary dust grains, visit Washington University Laboratory for Space Science
Copyright 1997 Dr. Sten Odenwald
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