The practical distinctions between asteroids and comets, viewed as products
of accretion on either side of the snow line, are less clear-cut than
previously understood. In this chapter, we discuss the numerous solar system
populations which have physical and dynamical properties that conflict with any
simple diagnosis of their nature and origin. Studies of these so-called
"continuum" or "transition objects", which include many of the most intriguing
bodies in the solar system, have implications for a broad range of scientific
topics from the demise of comets and the activation of asteroids to the
production of interplanetary debris and the origin of the terrestrial planet
volatiles. We present an overview of the current state of knowledge concerning
the asteroid-comet continuum and discuss the numerous physical processes behind
the activity shown by small bodies in the solar system.Comment: 34 pages, 23 figures, Chapter in press for the book Comets III,
edited by K. Meech and M. Combi, University of Arizona Pres