The orbital history of two periodic comets encountering Saturn

Two recently discovered short-period comets (P/1997 T3 (Lagerkvist-Carsenty) and P/1998 U3 (Jäger)) were found, by means of numerical integrations, to have recently encountered Saturn, leading to drastic orbital changes. In both cases the orbit was transformed from a Saturn-dominated regime (roughly tangential to Saturn’s orbit) into a deep Jupiter-crossing orbit. For P/1997 T3 a close encounter to within 0.011 AU was identified in October 1954 from numerical integrations of the current orbit, taking into account the gravitational perturbations by all major planets from Mercury to Neptune and Pluto. Similarly, an approach to within 0.018 AU was found for P/1998 U3 in July 1991. For each comet 99 variational orbits and the current orbit were integrated backwards in time well beyond the dates of the close encounters with Saturn. All orbital evolutions showed a similar change in the orbital parameters, as given above for the nominal orbit. In order to further investigate the past orbital history, all orbits were integrated backwards in time for 10,000 years. At that time the majority of the orbits (92% and 87%, respectively) of comets P/Lagerkvist-Carsenty and P/Jäger had perihelion distances larger than 5.3 AU.