THE DIRECTION OF THE NORTH-POLE AND THE CONTROL NETWORK OF ASTEROID 951 GASPRA

A control network containing 19 points identified on Galileo images obtained during the October 1991 flyby was used to determine the direction of Gaspra's north pole. We find the right ascension and declination (in J2000 coordinates) to be alpha(o) = 9.5-degrees +/- 0.9-degrees, delta(o) = 26.7-degrees +/- 1.2-degrees. This result agrees with earlier determinations based on telescopic observations of Gaspra's lightcurve. We confirm that the rotation is prograde, but we lack the time base to improve the value of the rotation period of 0.2934197 days determined by lightcurve analysis (Magnusson et al. 1992). We propose a prime meridian (0-degrees longitude) that passes through the center of the 630-m-diameter crater Charax, a selection that places the prime meridian close to Gaspra's long axis. (C) 1994 Academic Press, Inc.