[Previous] | [Session 16] | [Next]
M.P. Egan, S.D. Price (AFRL/VSBC), E.F. Tedesco (TSI)
Infrared detection from space offers an invaluable adjunct to ground based visible searches for the discovery and characterization of Near Earth Objects (NEOs). The known Near Earth Objects are predominately highly reflective, presumably due to a discovery bias against dark objects inherent in visual surveys. For a given diameter, dark objects are at least a factor of four fainter in the visual than those with high albedo. Various analyses argue that the population of dark objects among the NEOs should be at least as great as the highly reflective objects. In the mid-infrared (defined to be between 5 and 35 \mum) the flux difference between high and low albedo objects is relatively small, with slightly more flux coming from the dark object. Passive emission from objects located in the inner solar system peaks in the mid-infrared as the natural consequence of the object being in thermal equilibrium with the incident sunlight An infrared NEO survey compensates for the bias of visible searches to preferentially discover high albedo objects. Additionally, visual to infrared colors of NEOs are markedly different from those of most stars. This provides a basis for a bulk filter that significantly reduces the onboard signal processing requirements for a space-based system. Infrared observations also reduce the uncertainty in estimating the size, and subsequently the mass, of an NEO. A geometric albedo must be assumed in order to calculate a diameter from the single band visual photometry obtained during discovery or follow-up astrometry. The estimated size is thus quite uncertain owing to the order of magnitude range in NEO geometric albedos. The modeling assumptions needed to convert an infrared observation into a diameter are more tightly constrained. An infrared observation combined with visual photometry provides the requisite information to accurately determine both the albedo and size. Since the estimate of the NEO mass depends on volume, the determinations of NEO mass from infrared derived diameters are about an order of magnitude more certain than that estimated from visible photometry.
The author(s) of this abstract have provided an email address for comments about the abstract: egan@pldac.plh.af.mil