Cosmic Dust: Collection and Research

The term as used here refers to particulate material that exists or has existed in the interplanetary medium as bodies smaller than 1 mm. The particles can be collected both in space and in the terrestrial environment, and they are a valuable resource of meteoritic material. The dust samples are complementary to the traditional meteorites that were much larger meteoroids in space. Because of their size, the analysis of collected dust particles is more difficult and limited than studies of meteorites. Nevertheless, collected dust samples are being vigorously investigated for two fundamentally important reasons. The first is that the most friable extraterrestrial materials can only be collected in the form of dust. Highly fragile materials cannot survive hyper velocity entry into the atmosphere in chunks as large as conventional meteorites. Most cometary meteoroids are known to be fragile, and dust collection is the only Earth­ based technique for obtaining typical cometary solids. The second reason why dust is important is that it is very abundant. Meteorites are exceedingly rare, but cosmic dust is so common that quite literally every footstep a person takes contacts a fragment of cosmic dust. Dust is so abundant that, with appropriate techniques, it can be recovered from historical deposits in deep-sea sediments and collected in real time in space and in the stratosphere. Stratigraphic layers in sediments record a continuous history of the terrestrial accretion of space debris that extends beyond 108 yr ago. This record can be searched for temporal changes in the meteoroid complex, such as might occur during fluctuations in the number of comets in the inner solar system or during passage of the solar system through an interstellar cloud. Effects of isolated events, such as the terrestrial impact of a large body, are also contained in sediments. The flux