Historical Background

This meeting is about dust in our Solar System and Other Planetary Systems. Planets have been discovered in about 30 nearby systems, but in these we have not as yet observed dust. On the other hand, a number of young stars are known to have a dust disk about them, but in these direct detection of planets is absent. At present, our system is the only one where dust and planets, as well as comets and asteroids to provide a source for the dust is present. Many phenomenon show the presence of the interplanetary dust complex, the zodiacal light, grains captured in the near-Earth environment as well as a number of in-situ measurements from spacecraft both in Earth orbit and in transit to other regions of the Solar System. We start the discussion with proof that must have been visible to humans since pre-history, namely the streaks of light crossing the sky from time to time, popularly called shooting stars, but more correctly known as meteors. Indeed, many of the ancient Chinese, Japanese and Korean records, talk of stars falling like rain, or many falling stars. A detailed account of these early reports can be found in the work of Hasegawa [1]. The same general thought probably gave rise to the English colloquial name for meteors, namely Shooting Stars. In paintings of other events, meteors were often shown in the background (see for example [2]). These historical recordings are very valuable, for they show that the Perseids for example have been appearing for at least two millenia. Recording and understanding are however two different things so that the interpretation of these streaks of light as interplanetary dust particles burning in the upper atmosphere is somewhat more recent. The reason probably lies in the belief that the Solar System was perfect with each planet moving on its own well determined orbit. Such beliefs left no room for random particles colliding with the planets, especially the Earth. Meteors were thus regarded as some effect in the atmosphere akin to lightning, hence the name. About two centuries ago the situation changed. First, there were a number of well observed meteorite falls where fragments were actually recovered. This at least proved that rocks could fall out of the sky though it did not by itself prove that they had originated from interplanetary space, however, as more observations of meteors took place, so thoughts changed. The measurement of the height of meteors as about 90km by Benzenberg & Brandes in 1800 [3] in essence spelt the end of the lightning hypothesis. When Herrick (1837, 1838) [4,5] demonstrated that showers were periodic on a sidereal rather than a tropical year, the inter-planetary rather than terrestrial in origin was proved.

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