Dynamical origin of the asteroid (25143) Itokawa: the target of the sample-return Hayabusa space mission

Abstract

Aims. We have studied numerically the origin and dynamical evolution of the asteroid (25143) Itokawa on which a Japanese space probe landed and may have collected a sample. The return to Earth is planed in 2010. Methods. To estimate the most probable source of Itokawa, we have used the most recent model of the Near-Earth Object population, which allows us to relate the orbital parameters of a NEO to the different identified source regions of the NEO population. Results. The two source regions that are the most likely to transport an object to Itokawa's orbit are the ν 6 secular resonance in the main belt and at a lower level of probability the Mars-crosser population. This result is consistent with the spectral characteristics of Itokowa, identified as S-type, which is the dominant spectral type of objects in these sources. In a previous study, we had found that its most likely fate may be an impact with the Earth on a million year timescale. Here, we show that its evolution is consistent with the typical evolution of asteroids coming from the identified source and which are extracted in the Earth-crossing zone by planetary encounters. Conclusions. We conclude that Itokawa is a typical NEO, which probably arrived at its orbit from the main belt through the ν 6 channel. It belongs to the most common spectral-type in the inner Solar System. Therefore, unless this asteroid had a peculiar collisional history, the data obtained by the satellite Hayabusa will clarify some properties representative of the S-type NEO population.