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G. Black (U. Virginia), D. Campbell (Cornell/NAIC)
We report on progress to use a radio interferometer, the NRAO Very Long Baseline Array (VLBA), to image near Earth asteroids as they are illuminated by the Arecibo Observatory's S-band radar. By measuring the plane-of-sky brightness distribution of the target under the radar's illumination, this method will be able to provide direct, unambiguous spatial resolution of order 100~m which for many objects is sufficient to grossly define their shape, map large scale reflectivity variations, and measure the absolute orientation of the projected spin axis. With receiving antenna spacings of several thousands of kilometers, the potential resolution obtainable with the VLBA at the Arecibo wavelength of 13~cm is on the order of a few milli-arcseconds; several orders of magnitude smaller than typical ground-based telescopic observations. In addition, astrometry of these quickly moving objects at this milli-arcsecond level can greatly reduce orbit uncertainties.
This technique has been used to observe two near Earth asteroids, 2000~EW70 and 2002~NY40, during their recent close passes to Earth. The first asteroid was clearly detected; however, a useful correlation on either object is still in progress. A major limitation is the configuration of the hardware correlator which doesn't allow adequate frequency resolution and complicates incorporating a model of the near-field geometry. A solution to these difficulties is now available as a specialized computer interface designed to transfer the raw data into a portable format thereby bypassing the correlator and allowing for a more flexible correlation in software on another platform. Testing of this machine and the subsequent software correlation are currently underway.
The National Radio Astronomy Observatory (NRAO) is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the NSF.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.