Possible thermal metamorphism on the C, G, B, and F asteroids detected from their reflectance spectra in comparison with carbonaceous chondrites

Reflectance spectra (0.3-2.6μm) of the C, G, B, and F asteroids and carbonaceous chondrites are compared in detail. Mixing calculations of 13 carbonaceous chondrite powders including three unusual CI/CM meteorites are done to characterize reflectance spectra of the 23 C, G, B, and F asteroids. Similar calculations are done with Murchison (CM2) samples heated at 400-1000℃. Both of two sets of calculations show that the C, G, B, and F asteroids may contain a significant amount of thermally metamorphosed materials. Comparison of ultraviolet absorption strengths between 160 C, G, B, and F asteroids and 21 carbonaceous chondrite powders suggests that surface minerals of most of those asteroids are thermally metamorphosed at temperatures around 600-1000℃