Physics
Scientific paper
Jan 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004adspr..33.1548p&link_type=abstract
Advances in Space Research, Volume 33, Issue 9, p. 1548-1557.
Physics
Asteroids, Regolith, Mineralogy
Scientific paper
The physical characteristics of asteroid surfaces are best defined by direct measurements, few of which currently exist. Thus, inferences from indirect observations must be made. From the limited visible and radar imagery heavy cratering marks the asteroid surfaces and the surfaces are rough at all scales. For those asteroids with both a size and mass determination, only the largest bodies have bulk densities close to those expected from their meteoritic analogs. The smaller asteroids have large-scale porosities of 20% and greater; the objects with highest macroporosity are likely to be rubble piles while the denser ones may be heavily fractured coherent objects. The regoliths on the larger asteroids appear to be at least centimeters deep, while infrared measurements on the smaller objects argue for either a much thinner regolith or a bare surface; although direct imagery on the modest sized near-Earth asteroid 433 Eros indicates a regolith that is meters deep. Visual and infrared spectra clearly show that the silicates olivine and pyroxene are present on many asteroids and indicate the spectral signature of hydrated minerals in several low Albedo asteroids. Disk integrated photometry and radiometry provide clues as to the surface porosity and roughness and the fraction of surface covered by craters. Microwave, radio and radar measurements can penetrate the surface regolith, yielding information on the particle size distribution, and the nature of the underlying material. Modeling of the radiative transfer within the surface and deeper layers of an asteroid is required to accurately interpret these disk integrated measurements in terms of realistic physical parameters. Although the modeling has become sophisticated, additional components as well as more extensive and accurate measurements are required to derive an unambiguous picture of the asteroid surface layers from the indirect observations.
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