The existence of a planet beyond 50 AU and the orbital distribution of the classical Edgeworth-Kuiper-Belt objects

We study the effects of a Mars-like planetoid with a semimajor axis at about similar to60 AU orbiting embedded in the primordial Edgeworth-Kuiper belt (EKB). The origin of such an object can be explained in the framework of our current understanding of the origin of the outer Solar System, and a scenario for the orbital transport mechanism to its present location is given. The existence of such an object would produce a gap in the EKB distribution with an edge at about 50 AU, which seems to be in agreement with the most recent observations. No object at low eccentricity with semi-major axis beyond 50 AU has been detected so far, even though the present observing capabilities would allow an eventual detection (B. Gladman et al. 1998, Astron. J. 116, 2042-2054; D. Jewitt et al. 1998, Astron. J. 115, 2125-2135; E. I. Chiang and M. E. Brown 1999, Astron. J. 118, 1411-1422; R. L. Allen et al. 2000, Astrophys. J. 549, 241-244; C. A. Trujillo et al. 2001, Astron. J. 122, 457-473; B. Gladman et al. 2001, Astron. J. 122, 1051-1066; C. A. Trujillo and M. E. Brown 2001, Astrophys. J. 554, 95-98). Finally, ranges for the magnitude and proper motion of the proposed object are given. (C) 2002 Elsevier Science (USA).