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A. A. Christou (Queen Mary and Westfield College, University of London, United Kingdom)
We have investigated numerically the evolution of near-Earth asteroids (3753) Cruithne, (3362) Khufu, 1989 VA, (10563) 1993 WD and 1994 TF2 that enter the coorbital regions of the Earth or Venus. A number of dynamical clones of these objects were integrated for a total timespan of 2 \times 105 yr. These are captured temporarily in the co-orbital resonance with either of these planets for several tens of thousands of years, a significant fraction of the integration timespan. The observed statistics of capture into the resonance imply a 50 % probability that these asteroids will be or have been Earth or Venus co-orbitals in the timescales relevant to the numerical integrations.
The libration characteristics of these objects agree with the theoretical predictions by (Namouni, Icarus 137, 293-314, 1999) and (Namouni, Christou & Murray, Physical Review Letters, submitted) concerning co-orbital motion at high eccentricity and inclination. The predicted libration modes, namely retrograde satellite orbits (RS), tadpoles (T), tadpole-retrograde satellite compounds (T-RS and RS-T) and horseshoe-retrograde satellite compounds (H-RS and RS-H) are found to occur in specific ranges of values for the argument of pericentre.
It is shown that encounters with the co-orbital planet are stable and result in transitions between different libration modes inside the resonance. Close approaches with other planets do not always eject the object from the resonance. This contributes to the observed longevity of co-orbital motion.
The author(s) of this abstract have provided an email address for comments about the abstract: A.Christou@qmw.ac.uk