Kuiper-Belt Objects in the Planetary Region: The Jupiter Family Comets

Jupiter-family comets (JFCs) are a dynamically distinct group with low orbital inclinations and orbital periods ?20 yr. Their origin has been shown computationally to be the Kuiper belt region beyond Neptune. Therefore studying the nuclei of these comets, as well as their coma species, can provide valuable insights into the nature of the kilometer-sized Kuiper belt ob- jects (KBOs). These include their size distribution, internal structure, and composition, as well as some hints at their likely surface features. Although JFCs are much closer to the Sun than KBOs, they are still very difficult to observe due to their intrinsic faintness and outgassing comae. However, observational studies are advancing rapidly and we are now starting to place valuable constraints on the bulk physical properties of these nuclei. In this chapter, we review some of the more important findings in this field and their relevance to KBO studies.