Near-infrared spectral behavior of space-weathered olivine with varying iron content

¹ Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China
² College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, PR China
³ Department of Earth Sciences, University of Hong Kong, Hong Kong 999077, PR China
⁴ Research Center for Planetary Science, College of Earth Science, Chengdu University of Technology, Chengdu 610059, PR China
⁵ CAS Center for Excellence in Comparative Planetology, Hefei 230026, PR China
⁶ State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an 710069, PR China

^★ Corresponding author; linhonglei@mail.iggcas.ac.cn

Received: 28 May 2024
Accepted: 12 August 2024

Abstract

Context. Space weathering alters the surfaces of airless celestial bodies, thereby modifying their spectra significantly. Olivine plays a crucial role in responding to space weathering on silicate planets. However, the spectral variations that occur in olivine with varying iron content as a result of space weathering conditions remain unclear.

Aims. We aim to systematically characterize the spectral variability of surface iron-rich olivine in the space weathering environments of Phobos and the Moon.

Methods. We conducted nanosecond pulsed laser irradiation experiments on a set of synthetic Fe-rich olivine (Fa29, Fa50, Fa71, and Fa100). The energy levels were simulated for Phobos and the Moon. We analyzed the available near-infrared (NIR) spectroscopy.

Results. We find that olivine with higher Fe content undergoes stronger weathering under the same irradiation energy, shifting absorption centers around 1.08 µm and 1.35 µm to longer wavelengths. When comparing the high energy and low frequency, spectral changes are more pronounced at low energy and high frequency. The olivine with the same iron content exhibits a more noticeable shift around 1.08 µm under various irradiation levels, while the band center around 1.35 µm remains stable.

Conclusions. When the same amount of radiation energy is received, changes in the spectrum are more noticeable at low energy and high impact frequency than at high energy and low impact frequency. The absorption position at ~1.35 µm is a good indicator of the Mg# value of space-weathered olivine.