Ceres: High-resolution imaging with HST and the determination of physical properties

Nine HST orbits have been used to image Ceres using the High Resolution Camera of the Advanced Camera for Surveys. Two hundred and fifty-nine images in three filters (F555W, F330W and F220W) were obtained covering the entire surface. Two visible features are readily apparent, a dark patch and a bright point. The bright spot was suitable for control point work enabling the spin axis (291° RA and 59° Dec.) and the latitude (14°N) of the bright point to be determined. Limb accuracies of approaching 0.1 pixel accuracy enabled the shape of Ceres to be determined to be rotationally symmetric with a short axis of 909 km and a long axis of 975 km. Analysis of these images is preliminary and continues to be refined.