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J.-Y. Li, M. F. A'Hearn, L. A. McFadden (University of Maryland)
Disk-resolved photometric analyses primarily using Hapke's scattering theory have been carried out for four objects: asteroid (433) Eros, comet 19P/Borrelly, asteroid (1) Ceres, and comet 9P/Tempel 1.
Near Earth Asteroid Rendezvous returned disk-resolved images of Eros at seven wavelengths from 450nm to 1050nm. The single-scattering albedo, w, was found to mimic the spectrum of Eros, with 0.33±0.03 at 550nm. The single-particle phase function parameter, g, is -0.25±0.02, and the roughness parameter, \bar\theta, is 28\circ±3\circ, both of which are wavelength-independent. The V-band geometric albedo of Eros is 0.23, typical for an S-type asteroid.
From the resolved images of Borrelly obtained by Deep Space 1 (DS1), the maps of its w, g, and \bar\theta have been constructed by modeling the reflectance terrain by terrain, with modeled averages of 0.057±0.009, -0.43±0.07, and 22\circ±5\circ, respectively. All three parameters show large variations across the surface. The 1-D temperature measurement from DS1 can be well described by the standard thermal model, with small areas adjusted for ice sublimation for observed water production rate.
HST images through three filters at 553nm, 335nm, and 223nm, covering more than one rotation of Ceres, were acquired. Its V-band lightcurve agrees with earlier ground-based observations. A strong absorption band centered at about 280nm is noticed. The w at V-band is modeled to be 0.073±0.002. The \bar\theta is modeled to be 44\circ±5\circ. The first surface maps for Ceres at three wavelengths are presented.
Deep Impact has returned resolved images of Tempel 1 at seven wavelengths from 350nm to 950nm. The whole-disk spectrum of the nucleus shows a red slope of 12%/1000 angstroms. Photometric modeling yields a w of 0.040 at 650nm, and a surface roughness of about 25\circ. Only about 50 are observed for the surface of Tempel 1.
The author(s) of this abstract have provided an email address for comments about the abstract: jyli@astro.umd.edu
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.