Jonathan Horner, a former summer student at Armagh (now at the University of Bern, Switzerland), Wyn Evans (University of Cambridge) and Mark Bailey have completed two papers on the dynamical evolution of outer solar system objects known as Centaurs. These are large, so-called `giant' comets, circulating on dynamically unstable orbits confined approximately between the orbits of Jupiter and Neptune. The first paper presents bulk statistics of the orbital evolution of an ensemble of 23,328 particles, derived from the observed sample, integrated for 3Myr either side of the present. These represent the orbits of 32 well-known Centaurs. The average half-life for the entire sample is 2.7Myr, ranging from as short as 0.5Myr up to more than 32Myr for the most stable objects. The computed transfer probabilities demonstrate the principal pathways through which these outer solar system objects move before being dynamically ejected or inserted on to short-period cometary orbits similar to those of the observed Jupiter family. The total number of Centaurs larger than 1km across is estimated to be approximately 44,000.
The second paper presents a more detailed investigation into the evolution of the individual objects, illustrating behaviours such as capture of Centaurs into Jovian Trojan orbits, repeated `bursts' of short-period cometary orbital evolution, capture into mean-motion resonances with the giant planets and so-called `Kozai' resonances, as well as traversals of the whole solar system. Roughly 60% of the largest Centaurs, such as (2060)Chiron, become short-period comets at some stage of their dynamical evolution. This is a typical feature of the Centaur population, a result which has important implications for understanding the origin and long-term evolution of interplanetary dust in the solar system and the number of Earth-crossing `asteroids' of high mass.