Abstract

Among the NEA binaries we can find nearly all taxonomic types. The formation of binary systems apparently does not depend on asteroid composition. If most of these systems do indeed evolve from some sort of spin-up mechanism (such as YORP) then the necessary mechanical state of the material can be reached from a wide range of starting compositions. I will review the relationship of taxonomy to composition, what can and cannot be concluded. The M-type class is of particular interest since there is some controversy about the various interpretations of the reflectance spectra. The time scales for evolution of binary systems depend heavily on the density and material properties, so consideration of the composition and mechanical properties may be important. The radar properties of NEA binaries can in some cases constrain the composition. Using the radar size and absolute magnitude we can estimate the albedo, independent of thermal properties. All these parameters vary widely for NEA binaries, challenging theories of their origin and evolution.