Abstract

Comets, like asteroids, are considered a threat to those on planet Earth. There is some belief that comets pose a substantially greater risk than asteroids. This chapter defined and described comets. The concept of great comets was discussed and exemplified. Vast numbers of ‘iceteroids,’ which may be understood as pre-cometary cosmic phenomenon, are thought to populate both the Kuiper Belt and the Oort Cloud. The number of comets was discussed. Comets have random orbits due to their composition and orbit and the implications of this phenomenon were explained. The devastating nature of a comet impact on the Earth was considered. It was noted that there will most likely be relatively little advance warning of the approach of a killer comet. The impressive durability of comets was discussed. The concept of a comet shower was postulated. Comet groups were discussed. The Rosetta study of the Churyumov-Gerasimenko comet was explained.