The Neutral Coma

Abstract

Since nearly all comets bright enough to be seen readily with the unaided eye also show prominent tails, and since these tails are much larger than the coma (even though their density is much lower), the tail is often thought of as the identifying characteristic of a comet and nearly all pre-telescopic depictions of comets show them dominated by the tail. On the other hand, as discussed in the previous chapter, the nucleus is the fundamental body of a comet and the source of all material in the coma and the tail. Nevertheless, it is only the transient existence of a coma that observationally distinguishes a comet from an asteroid and as such the coma is the observational essence of a comet. In this chapter and the next we will consider the production of the coma from the nucleus, the physical processes that occur in the coma, and the loss of material to the dust and plasma tails. There are two reasonably distinct components of the coma: The neutral gas and the dust; they will be considered in separate chapters.