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S. J. Ostro (JPL/Caltech)
Radar delay-Doppler measurements are powerful for refining asteroid orbits because they have extremely fine fractional precision and are orthogonal to optical angle astrometry. Radar detection of a newly discovered near-Earth asteroid (NEA) secures its orbit and can add centuries to the interval over which its close Earth approaches can accurately be predicted. With radar, refinement of orbits is so tightly coupled to physical characterization that almost every asteroid radar experiment that produces new information about a target's size, shape, rotation, and surface properties also furnishes astrometry for improving the ephemerides.
Delay-Doppler images of NEAs can achieve decameter resolution. Models derived from image sequences let one explore the evolution and stability of close orbits, with direct application to navigation of spacecraft and to investigation of impact-induced regolith redistribution. Radar signatures have been measured for more than 200 asteroids whose size and spin-period distributions span four orders of magnitude. Radar can reveal excited rotation states, contact-binary shapes, and binary systems, and has identified several NEAs in each of those categories. The radar binaries are yielding our first accurate estimates of the masses and densities of potentially hazardous asteroids.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.