ASTEROID 951-GASPRA - PRE-GALILEO PHYSICAL MODEL

Prior to the October 1991 encounter of 951 Gaspra, asteroids were the only class of Solar System objects not resolved by spacecraft images. Analysis of the data returned by the Galileo spacecraft will apply critical tests to many techniques developed during the past 50 years for deriving physical properties for several hundred asteroids. As a benchmark for comparison, we have applied these techniques to establish in advance our best estimates for Gaspra's properties. We estimate it has an elongated shape with a ratio between equatorial axes of about 1.5-1.7. Further, we derive its sidereal rotation period to be 0.2934197 ± 0.0000010 days with its spin vector pointing toward ecliptic coordinates λ0 = 20° ± 5°, β0 = +22° ± 5° (or less likely λ0 = 198° ± 5°, β0 = +13° ± 5°). © 1992.