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A. W. Harris (DLR, Berlin), M. Delbo (Obs. Turin), R. P. Binzel (MIT)
The main conclusions to date of our on-going program of thermal-infrared observations of near-Earth asteroids (NEAs) are presented. The evidence collected thus far suggests that relatively few NEAs in the size range covered by our program (D = 0.1 - 25 km) have large thermal inertias, implying that the majority of objects have significant insulating regoliths. The spread of albedos, pv, in the sample of some 30 objects studied to date is very large (0.02 - 0.55) and there is evidence of a trend of increasing albedo with decreasing size, at least among S-type NEAs. The mean albedo of the objects in the sample is much higher than that of observed main-belt asteroids, although the significance of this comparison with the present small sample and possible observational bias is not clear. Agreement with the albedos expected from the taxonomic classifications is good, with a few exceptions (e.g. two C-type NEAs appear to have albedos above 0.1). At least one object with a very low albedo may be an inactive cometary nucleus. Finally, some objects, including two binary NEAs, display unusually low color temperatures when observed at large phase angles, leading us to speculate that such objects may have peculiarly rough or irregular surfaces leading to preferential emission in the sunward direction and correspondingly less radiation being observed at high phase angles. This work is supported in part by the German Research Foundation (Deutsche Forschungsgemeinschaft).
The author(s) of this abstract have provided an email address for comments about the abstract: alan.harris@dlr.de
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.