31st Annual Meeting of the DPS, October 1999
Session 1. Asteroids: NEAR, Here and Over There
Contributed Oral Parallel Session, Monday, October 11, 1999, 9:00-10:00am, Sala Plenaria

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[1.02] NEAR Lightcurves of Eros: Evidence for Albedo Variation at Lons 240-300

B.E. Clark, J. Veverka, P.C. Thomas, J. Joseph, B.T. Carcich, P. Helfenstein (Cornell University), S. Murchie, D. Domingue (Johns Hopkins University Applied Physics Laboratory), M.S. Robinson (Northwestern University), W. Owen (Jet Propulsion Laboratory), W.J. Merline (Southwest Research Institute)

The NEAR spacecraft flew by asteroid 433 Eros in December, 1998, and obtained images of the surface (best resolution is about 400 meters/pixel). These images (obtained by the NEAR Multispectral Imager (MSI)) were used to derive a shape model. In addition, the images obtained at phase angles of 88 to 115 degrees during the flyby were used to modify the photometric model of Eros. The highest phase angle observations of Eros prior to the flyby were Earth-based, point source photometry provided by Harris et al. (personal communication) and were limited to phase angles less than 60 degrees.

We have used the post-flyby shape model and photometric model to predict the lightcurve of Eros as viewed from specific viewing angles. The viewing angles used correspond to actual viewing angles of lightcurve data obtained in flight by the MSI. The MSI data were taken in a series of 6 observations between November 1998 and May 1999 over which time the sub-observer latitude ranged from 56 degrees North to 9 degrees South and the sub-solar latitude ranged from 19 degrees South to 79 degrees South. In addition, we have obtained lightcurve data from Hicks et al. which were taken in August, 1998, at sub-observer latitude 57 degrees North, and sub-solar latitude 21 degrees North. The total phase angle range of these lightcurve data is 36-101 degrees. Our data covers a significant range in look angles and they should therfore be useful in performing a comparison between model predictions and observed measurements.

Comparisons between observed and modelled lightcurves reveal discrepancies up to 0.5 magnitudes that result from either 1) shape model inaccuracies or 2) albedo variations on the surface of Eros. We argue that the second alternative is much more likely. We present our analyses and make the case that Eros may have significant albedo features located at northern and southern latitudes between longitudes 240-300. These longitudes were only partly imaged during the NEAR flyby of December 1998.

The author(s) of this abstract have provided an email address for comments about the abstract: beth@astrosun.tn.cornell.edu

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