Spectral Reflectance Properties (0.3–2.5 μ m) of LL Ordinary Chondrites

Abstract Spectral characterization of asteroids relies on meteorite spectral calibration to constrain their surface mineralogy. We have conducted a comprehensive spectroscopic study of LL chondrites to shed light on the factors that control their reflectance spectra in the 0.3–2.5 μ m region. Our results show that the ratio of the area of an absorption feature in the 2 μ m region to that of Band I (termed the band area ratio (BAR)) decreases with increasing petrologic grade. Grain-size variations can cause systematic changes in the spectral slope, albedo, absorption depths, and BAR of LL chondrites. The chip spectra of LL chondrites have a blue spectral slope and shallow absorption depths when compared to their corresponding powder spectra. Phase-angle variation has a systematic effect on the spectral slope and albedo of LL chondrite spectra. The shock effect can cause systematic changes in the albedo and absorption depths of LL chondrites. Whether or not the metal/magnetic particles are removed has little effect on the spectra of LL chondrites. Terrestrial weathering significantly reduces the 0.5/0.6 μ m reflectance ratio of LL chondrites, but this ratio has no clear trend with weathering grade. We also applied these results to four well-known asteroid mission targets. Our results suggest that the spectral difference between smooth terrain and rough terrain of 25143 Itokawa may be due to the presence of fine-grained regolith in the smooth terrain. The contents of olivine and pyroxene in 4179 Toutatis, 99942 Apophis, and 469219 Kamo’oalewa are comparable to those in L chondrites, LL chondrites, and LL chondrites, respectively.