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.
Keywords: Advance warning, ballistic missile, coma, comets, dust, gas, gravel, great
comets, hydrogen, ice, inert, interstellar grains, ion, ISON, lead time, microscopic
voids, Naval Research Institute, particulate matter, perihelion, random orbit.
