Submitted to Astronomical Journal

Explaining the origin of the orbit of 2000 CR105 (a ∼ 230 AU, q ∼ 45 AU) is a major test for our understanding of the primordial evolution of the outer Solar System. Gladman et al. (2001) showed that this objects could not have been a normal member of the scattered disk that had its perihelion distance increased by chaotic diffusion. In this paper we explore four seemingly promising mechanisms for explaining the origin of the orbit of this peculiar object: (i) the passage of Neptune through a high-eccentricity phase, (ii) the past existence of massive planetary embryos in the Kuiper belt or the scattered disk, (iii) the presence of a massive trans-Neptunian disk at early epochs which exerted tides on scattered disk objects, and (iv) encounters with other stars. Of all these mechanisms, the only one giving satisfactory results is the passage of a star. Indeed, our simulations show that the passage of a solar mass star at about 800 AU only perturbs objects with semi-major axes larger than roughly 200 AU to large perihelion distances. This is in good agreement with the fact that 2000 CR105 has a semimajor axis of 230 AU and no other bodies with similar perihelion distances but smaller semi-major axes have yet been discovered. The discovery of 2003 VB12, (a = 450 AU, q = 75 AU) announced a few days before the submission of this paper, strengthen our conclusions. Subject headings: Origin, solar system; planetary formation; Kuiper belt objects; Trans-Neptunian objects; Celestial mechanics