Estimation of the space weathering timescale on (25143) Itokawa: Implications on its rejuvenation process

Abstract

Context. The space weathering timescales of near-Earth S-type asteroids have been investigated using several approaches (i.e., experiments, sample analyses, and theoretical approaches), yet there are orders of magnitude differences. Aims. We aim to examine the space weathering timescale on a near-Earth S-type asteroid, Itokawa, using Hayabusa/AMICA images, and further investigate the evolutional process of the asteroid. Methods. We focused on bright mottles on the boulder surfaces generated via impacts with interplanetary dust particles (IDPs). We compared the bright mottle size distribution with an IDP flux model to determine the space weathering timescale. Results. We found that the space weathering timescale on Itokawa’s boulder surfaces is 103 yr (in the range of 102–104 yr), which is consistent with the timescales of space weathering by light ions from the solar wind. Conclusions. From this result, we conclude that Itokawa’s surface has been weathered rapidly in 103 yr but portions of the surface are exposed due to seismic shaking that was triggered by a recent impact, which created the Kamoi crater.