¹Edward A. Cloutis et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.116952]
¹Centre for Terrestrial and Planetary Exploration, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada
Copyright Elsevier

Four carbonaceous chondrite (CC) meteorites – MET 00432, Tagish Lake, Tarda, and WIS 91600 – have been proposed to be members of a CC grouplet, hereafter termed the Carbonaceous Tagish Lake Grouplet (CTG). We investigated their possible affinities via a spectral reflectance-focused study of them, as chips and variously sized powders. We also considered possible spectrum-altering effects of space weathering and composition of the organic component on such red-sloped spectra. Ultraviolet-region spectra (200-400 nm) exhibit absorption features attributable to unspecific Fe2+-O and/or Fe3+-O charge transfers, possibly due to Fe-rich phyllosilicates. Both albedo and spectral slope vary as a function of grain size. The 0.35-2.50 μm interval is characterized by dark, variably red-sloped spectra with low albedos in the visible region (<6% reflectance at 0.550 μm). Spectral slopes are redder for powders than slabs or chips. CTG spectra also exhibit shallow (<4% deep) absorption bands attributable to known components, such as magnetite and phyllosilicates, particularly in the 1 μm region. Spectral analysis of an extensive suite of phyllosilicate+opaque mixtures suggests that only a subset of CTG opaque components can cause darkening and overall red spectral slopes, in particular low H/C ratio carbonaceous compounds. Other opaque components, such as iron sulfides, magnetite and other carbonaceous materials, some of which are red-sloped when pure, cause spectral bluing or only slight spectral reddening. Albedo and spectral slopes and shapes are affected by physical properties, such as grain size, as well as the types, compositions, abundances, dispersion, and grain sizes of opaque components. At longer wavelengths (to 14 μm), CTG spectra exhibit a number of absorption features that can be related to their silicate, carbonate, and organic components. A prominent absorption feature is present in the 2.7-3.1 μm region attributable to phyllosilicates ± H2O, some of which is likely attributable to terrestrial alteration. Petrological, mineralogical, and isotopic information provide support for these meteorites having strong affinities to each other and comprising a grouplet. Additional CTG meteorites may lurk among the many tens of CCs that have been incompletely characterized.