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

¹ Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
² SNU Astronomy Research Center, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
e-mail: jin@astro.snu.ac.kr; ishiguro@snu.ac.kr

Received: 23 June 2022
Accepted: 1 September 2022

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.