Space Observations

Abstract

As pointed out in the introductory chapter, dust, not just neutral but charged dust, is believed to be ubiquitous in nature, although opinions diverge about how important charged dust indeed is. However, before embarking in the following chapters on various aspects of wave phenomena in dusty space plasmas, where we are among the believers, it is extremely useful to collect some of the available data and separate what is really known from exhilarating flights of fancy. This is at the same time a sobering exercise, because many characteristics of dust grains in space plasma environments are still unknown, to say the least. Spurred by solar system observations that can only be explained by the essential presence of charged dust, since purely gravitational forces are clearly insufficient, theoreticians have leapt ahead of the available data and explored many exciting but maybe speculative avenues. These need to be calibrated to what is accepted observational knowledge, and it is for this purpose that the present chapter is included here, although I will also sin in the next chapters, when reviewing the different modes studied in the literature and thought to be important in dusty plasma research.