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.
The above photograph is of a collected interplanetary dust particle. For more information visit the Stardust Program web site.For more about interplanetary dust particles, visit Scott Messenger's pages at Washington University Laboratory for Space Science
In a recent letter to me about these particles on November 25, 2000, Dr. Scott Messenger writes:
Nobody has succeeded in isolating an interstellar silicate grain, but the best candidates we have so far are "GEMS" - inclusions commonly found in cometary dust. The difference between 'interstellar' and interplanetary dust is not at all clear from your answer. The picture you show is of an interplanetary dust particle (which I took with an scanning electron microscope). Interplanetary dust is simply a smaller version of what meteorites are - chunks of minor planets (asteroids and comets). They are different in detail from meteorites though, which means that they by and large come from different bodies. Probably, the IDP you show is from a comet. That dust particle may CONTAIN grains of interstellar dust, and probably contains some primordial interplanetary dust, from the era of solar system formation. Meteorites are known to contain individual grains of stardust and ancient solar nebular dust.
You are talking about *ancient* Solar System dust when you answer the original question. This is *not* the same thing as the SEM picture you show. Since you do not label the figure, the impression to the reader is probably that this is a piece of *ancient* Solar System dust. It is in fact a modern grain of interplanetary dust - a piece of a larger solar system body...It is not possible to collect ancient solar system dust or ancient stardust other than from larger bodies, like meteorites or comets. I don't feel that your essay is incorrect, simply a bit unclear. Secondly, you seem to imply that (all?) of the ancient solar system dust is stardust. Most of the ancient solar system dust surviving in meteorites formed in the solar system, with only a small fraction having a stellar origin. But that's a minor point, and is a can of worms.
I understand that you are a professional astronomer, but I thought you may not have been exposed to much in the way of laboratory studies of interplanetary dust particles (IDPs). The laboratory study of IDPs is sort of an obscure field even among the professional astronomers whom I have met.
Copyright 1997 Dr. Sten Odenwald
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