Limb darkening of meteorites and asteroids |
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| Authors: | Linda M French J Veverka |
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| Institution: | Laboratory for Planetary Studies, Cornell University, Ithaca, New York 14853, USA |
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| Abstract: | This paper presents the results of a laboratory study of the limb darkening, near opposition, of the carbonaceous chondrites Orgueil (C1), Murchison (C2), and Allende (C3), the ordinary chondrite Bruderheim (L6), and a stainless-steel powder. These materials represent possible analogs for the surface materials of C, S, and M asteroids respectively. At low phase angles, the limb-darkening behavior of all materials studied is well represented by Minnaert's law. For carbonaceous chondrites, the Minnaert limb-darkening parameter k is nearly independent of wavelength for wavelengths between 0.4 and 0.9 μm, with a typical value of k = 0.55. The reflectance parameter, B0, varies from 0.045 to 0.065 over the same range of wavelengths. Both k and B0 are larger for the stainless-steel powder and the ordinary chondrite, due to the increased importance of multiple scattering in the surface layer. If no limb darkening were present, k would equal and the geometric albedo (p) of an asteroid would equal the normal reflectance of its surface material. For bodies whose surface material is appreciably limb darkened, the geometric albedo measured at the telescope will be lower than the true normal reflectance of surface material; we estimate that for S and M objects rn ? 1.05 p. In the case of nonspherical asteroids, because the distribution of incidence and emission angles varies as the asteroid rotates, the geometric albedo must change with aspect. If limb darkening is not considered when interpreting asteroid light curves, the values of b/a derived will be too extreme. This effect is probably too small to be observed for C asteroids, because of their intrinsically low reflectances, but could be appreciable for S and M objects. |
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| Keywords: | To whom correspondence should be addressed |
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