Mathematics – Probability
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005dps....37.1412y&link_type=abstract
American Astronomical Society, DPS meeting #37, #14.12; Bulletin of the American Astronomical Society, Vol. 37, p.638
Mathematics
Probability
Scientific paper
We have studied numerically the dynamical evolution of the asteroid (25143) Itokawa from which, for the first time, a sample is planed to be brought back to Earth in 2007 by the Japanese space probe HAYABUSA launched in May 2003. Beause of the chaotic nature of Itokawa's orbit, we performed a statistical study of its long term dynamics by integrating numerically over their whole dynamical lifetimes several initially ``indistinguishable" orbits (``clones"), obtained by small variations of the nominal initial conditions. Integrations were computed with a Bulirsh-Stoer integrator and included the gravitational perturbations of all planets from Mercury to Neptune. The results show that all clones are mostely affected by planetary close approaches during their evolutions, and many of them finally collide with either Venus or the Earth. A few of the surviving ones are eventually transported in one of the powerful dynamical mechanisms, such as the nu6 resonance, which sends them into the Sun or ejects them outside Saturn's orbit. Half of the evolutions have a lifetime smaller than 8 Myr, which is consistent with the median lifetime of the whole observed NEO population. We finally performed the same integrations but added the Yarkovsky force, which can act effectively on objects having Itokawa's physical properties. The results show that the strength and frequency of planetary close approaches are too high to let the Yarkovsky force build up its effect so that no statistical difference is found with the purely gravitational integrations. We conclude that Itokawa is not a dynamically peculiar body and may well represent a typical NEO, which probably came on its orbit from the main belt, as suggested by its S spetral type which the most common type in the inner Solar System. Therefore, unless this asteroid had a peculiar collisional history, its samples may well provide some representative properties of the whole S-type NEO population. Further studies are under way to determine its origin and impact probability with the Earth.
Michel Pascal
Yoshikawa Makoto
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