Shape model and rotational state of dwarf planet Ceres from Dawn FC stereo images

Abstract

In February 2015 during the Ceres Approach phase, 76 clear filter images were acquired to investigate the rotational characteristics of Ceres. During two observation sequences (RC1 and RC2) the entire illuminated surface of Ceres was mapped in visible wavelengths as a rotational movie with a nominal image scale of about 8 km/pixel and 4 km, respectively. We applied our stereo-photogrammetric processing described above and derived a 3D control point network. From that we determined the spin rate of Ceres to be 952.1532 degree/day, which perfectly matches the previous determination from ground-based data [7]. Additionally we refined Ceres’s spin axis orientation to be: right ascension = 291.62° ± 0.2°, declination = 66.47° ± 0.1°, which matches within error the values formerly determined from Earth-based observations [8]. Finally we adjusted the nominal orientation and applied dense multi-image matchingto compute a dense surface point cloud. From that we derived a first surface model of Ceres (see Figure 1) with a lateral spacing of about 4 km/pixel and mean point accuracy of 800 m. The reference coordinate system used to depict the shape model is defined by spin axis orientation (values above) and the prime meridian definition with W0=170.90° [8]. This reference frame will be finally fixed using Survey orbit observations.