Distinguishing between Shock-Darkening and Space-Weathering Trends in Ordinary Chondrite Reflectance Spectra
Space-weathering as well as shock effects can darken meteorite and asteroid reflectance spectra. We present a detailed comparative study on shock-darkening and space-weathering using different lithologies of the Chelyabinsk LL5 chondrite. Compared to space-weathering, the shock processes do not cause significant spectral slope changes and are more efficient in attenuating the orthopyroxene 2 μm absorption band. This results in a distinct shock vector in the reflectance spectra principal component analysis, moving the shocked silicate-rich Chelyabinsk spectra from the S-complex space into the C/X complex. In contrast to this, the space-weathering vector stays within the S complex, moving from Q type to S type. Moreover, the 2 μm to 1μm band depth ratio (BDR) as well as the 2 μm to 1μm band area ratio (BAR) are not appreciably affected by shock-darkening or shock melting. Space-weathering, however, causes significant shifts in both BDR and BAR toward higher values. Application of the BDR method to the three distinct areas on the asteroid Itokawa reveals that Itokawa is rather uniformly space-weathered and not influenced by regolith roughness or relative albedo changes. © 2020. The Author(s). ; We would like to thank Juan Sanchez for his help with PCA classification, Radoslaw Michallik for his help with the SEM images, and Eric MacLennan for his help with digitizing Figure 9. This research is supported by the Academy of Finland project No. 293975 and the Ministry of Education, Youth and Sports of the Czech Republic grant No. LH12079, NASA SSERVI Center for Asteroid and Lunar Surface Science (CLASS), MINOBRNAUKI project 5.3451.2017/4.6, Minobrnauki project FEUZ-2020-0059, and Act 211 of the Government of the Russian Federation, agreement No. 02. A03.21.0006, and with institutional support RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences. The University of Winnipeg's C-TAPE was established with funding from the Canada Foundation for Innovation, the Manitoba Research Innovation Fund, the ...