THE ORBIT OF 1999UG5Effects of the close approach to Saturn in 2002
The effects of the close approach to Saturn in 2002, and another milder approach in 1815, can be observed in these graphs, producing abrupt "jumps" in the otherwise normal periodic perturbations and small secular drifts. The minimum distance between Saturn and 1999UG5 will be 0.458 AU on May 22, 2002. Perturbations are of two types: secular (cumulative) and periodic, or usually a combination of both, the amplitude of a particular periodic perturbation increasing with time. It usually happens that a secular drift is really a periodic perturbation of very long period, so before reaching conclusions about the instability of Asbolus' orbit, plots for longer timespans and a better orbit determination are needed. The effects shown here can be compared with similar graphs of the orbit of 1998SG35 and the orbit of Asbolus, and show that Asbolus has a much more stable orbit than both UG5 and SG35; in fact, no other centaur (with the possible exception of 1995SN55, for which we'll have to wait for a better orbit estimation) shows variations of such magnitude in such a short timespan, or so close to the present, as SG35 and UG5. As can be seen from the plot of the semimajor axis, the encounter "shrinks" the orbit of 1999UG5, reducing its period of revolution from 45 years to 40 years. The elements used for the numerical integration were taken from the MInor Planet Center database and are fitted to 110 observations covering 2 oppositions. A similar study of
the orbital changes suffered by Chiron in a minor encounter with Saturn
in 1899 is in preparation.
Figure 1: semimajor axis
Figure 2: sidereal period of revolution
Figure 3: orbital eccentricity
Figure 4: longitude of perihelion
Figure 5: orbital inclination
Figure 6: longitude of the ascending node

