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

Abstract

Context. The space weathering timescale of near-Earth S-type asteroids has been investigated by 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. As a result, we found that the space weathering timescale on Itokawa's boulder surfaces is 10$^3$ years (in the range of 10$^2$-10$^4$ years), which is consistent with the timescale of space weathering by light ions from the solar wind. Conclusions. From this result, we conclude that Itokawa's surface has been weathered shortly in 10$^3$ years but portions of the surface are exposed via seismic shaking triggered by a recent impact that created the Kamoi crater.