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

¹ Observatoire de la Côte d'Azur, UMR 6202 Cassiopée/CNRS, BP 4229, 06304 Nice Cedex 4, France e-mail: Patrick.Michel@obs-azur.fr
² Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan

Received: 7 October 2005
Accepted: 22 December 2005

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  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  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.