LIMITATIONS ON THE EXISTENCE OF A 10TH PLANET

The orbits of 14 known Trans-Neptunian Objects were numerically integr ated for time intervals of up to 10(7) yr in the presence of an imagin ary tenth planet with a mass equal to that of Neptune as well as the k nown outer planets. This ''planet'' was placed on various hypothetical orbits. The results of these integrations allow the determination of whether or not the Trans-Neptunian Objects remained stable for the giv en interval. On the assumption that the real objects have remained sta ble, limits can be placed on possible orbits for this hypothetical ten th planet. It transpires that if all investigated Trans-Neptunian Obje cts are to be stable, then the orbit of the tenth planet, if near the ecliptic, must have a semi-major axis in excess of 70 AU. Increasing t he eccentricity of the orbit of this hypothetical tenth planet increas es the level of instability while in contrast, increasing the inclinat ion aids stability and for highly inclined orbits of the hypothetical tenth planet, no realistic restriction on the semi-major axis of the o rbit exists through the existence of Trans-Neptunian Objects. (C) 1997 Elsevier Science Ltd.