Constraints to Uranus' Great Collision .2.

It is generally assumed that the Jovian planets share common features as a consequence of similar formation and evolutionary processes. Nevertheless, Uranus is the only one without observed outer satellites and with a large spin axis inclination. This obliquity is usually attributed to a great tangential collision with another protoplanet during the stage of planetary formation. This collision could also justify the lack of outer satellites of the planer. Dynamical constraints to Uranus' Great Collision are settled in connection with the observational evidence. The transfer of angular momentum at collision is considered, which allows the two free parameters of the problem (the impactor incident velocity v(i) and its mass m(i)) to be reduced to one, giving a relation v(i)(m(i)). By means of simplified energy considerations, it is also possible to set an upper bound on the impactor velocity as a function of its mass. In addition, the most probable situation is considered in which the impactor would have been bound to the Solar System. In this case the maximum allowed value for v(i) is similar to 31.54 km s(-1), being the minimum possible mass to satisfy the required angular momentum to tilt Uranus similar to 1-1.1 m(+). The lower allowed value for v(i) corresponds to a body undergoing a temporary satellite capture. This value is similar to 22 km s(-1), being the minimum mass for this body similar to 1.5 m(+). On the other hand how the orbits of hypothetical, preexisting satellites of Uranus are unbound as a consequence of the energy injected by the collision is considered. The relevant result is that any massless particle orbiting Uranus beyond similar to 70-90 planetary radii was probably swept out from the system. A further intensive search for faint objects orbiting Uranus beyond 70 planetary radii would provide a constraint to the Great Collision Hypothesis. (C) 1997 Elsevier Science Ltd.