Dynamical and physical properties of comet--asteroid transition objects

In the last few years it has been pointed out that, from both physical and dynamical point of view, it is becoming more and more difficult to distinguish comets from asteroids and indeed there are some examples of small bodies first designated as comets which had, later, to be reclassified as asteroids and vice versa (Hartmann et al., 1990; McFadden, 1994). In order to investigate the evolutionary path of comets and asteroids in terms of both dynamical and physical properties, we performed spectroscopic observations of three objects discovered between 1990 and 1995 -- (6042) 1990 WW_2, (6144) 1994 EQ_3, and 1995 QY_2 -- and analyzed their orbital evolution. Obtained spectra show the typical trend of low-albedo, ``primitive'' objects, similar to those of outer-belt asteroids and comet nuclei. The dynamical analysis shows that (6042) 1990 WW_2 is on a stable orbit with a typical asteroidal behavior; (6144) 1994 EQ_3 is on a Jupiter-crossing chaotic orbit and in the past could have spent some time in a Jupiter's horsehoe orbit; 1995 QY_2 is a Mars crosser and librates about the 15/7 resonance with Jupiter and has a 40% chance to make a transition from asteroid to comet orbit over a timescale of about 3--5*E(5) yr. Based on observations carried out at the European Southern Observatory (ESO), La Silla, Chile.