Itokawa's cratering record as observed by Hayabusa: Implications for its age and collisional history

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.04.002 Byline: P. Michel (a), D.P. O'Brien (b), S. Abe (c), N. Hirata (d) Keywords: Asteroid Itokawa; Asteroids; surfaces; Cratering; Geological processes; Near-Earth objects Abstract: In this paper, we study cratering and crater erasure processes and provide an age estimate for the near-Earth Asteroid (25143) Itokawa, the target of the mission Hayabusa, based on its crater history since the time when it was formed in the main belt by catastrophic disruption or experienced a global resetting event. Using a model which was applied to the study of the crater history of Gaspra, Ida, Mathilde and Eros [O'Brien, D.P., Greenberg, R., Richardson, J.E., 2006. Icarus 183, 79-92], we calculate the time needed to accumulate the craters on Itokawa's surface, taking into account several processes which can affect crater formation and crater erasure on such a low-gravity object, such as seismic shaking. We use two models of the projectile population and two scaling laws to relate crater diameter to projectile size. Both models of the projectile population provide similar results, and depending on the scaling law used, we find that the time necessary to accumulate Itokawa's craters was at least [approximately equal to]75 Myr, and maybe as long as 1 Gyr. Moreover, using the same model and similar parameters (scaled accordingly), we provide a good match not only to Itokawa's craters, but also to those of Eros, which has also been imaged at high enough resolution to give crater counts in a similar size range to those on Itokawa. We show that, as for Eros, the lack of small craters on Itokawa is consistent with erasure by seismic shaking, although for Itokawa, the pronounced deficiency of the smallest craters ( Author Affiliation: (a) UMR 6202 Cassiopee, University of Nice-Sophia Antipolis, CNRS, Observatoire de la CA[acute accent]te d'Azur, BP 4229, 06304 Nice Cedex 4, France (b) Planetary Science Institute, 1700 E. Ft. Lowell, Suite 106, Tucson, AZ 85719, USA (c) National Central University, 300 Jhongda Rd, Jhongli City, Taoyuan 320, Taiwan (d) Department of Computer Software, The University of Aizu, Aizu, Japan Article History: Received 28 September 2007; Revised 2 April 2008