  In an effort to understand the origin of the Main Belt Comets (MBCs) 7968
Elst-Pizzaro, 118401, and P/2005 U1, the dynamics of these three icy asteroids
and a large number of hypothetical MBCs were studied. Results of extensive
numerical integrations of these objects suggest that these MBCs were formed
in-place through the collisional break up of a larger precursor body.
Simulations point specifically to the Themis family of asteroids as the origin
of these objects and rule out the possibility of a cometary origin (i.e. inward
scattering of comets from outer solar system and their primordial capture in
the asteroid belt). Results also indicate that while 7968 Elst-Pizzaro and
118401 maintain their orbits for 1 Gyr, P/2005 U1 diffuses chaotically in
eccentricity and becomes unstable in ~20 Myr. The latter suggest that this MBC
used to be a member of the Themis family and is now escaping away. Numerical
integrations of the orbits of hypothetical MBCs in the vicinity of the Themis
family show a clustering of stable orbits (with eccentricities smaller than 0.2
and inclinations less than 25 deg.) suggesting that many more MBCs may exist in
the vicinity of this family (although they might have not been activated yet).
The details of the results of simulations and the constraints on the models of
the formation and origins of MBCs are presented, and their implications for the
detection of more of these objects are discussed.
