On January 25, the NASA Dawn spacecraft imaged the dwarf planet Ceres at a distance of 237,000 km (22 km/pixel), exceeding the resolution obtained by Hubble a decade earlier. This is among a sequece of images obained for navigation purposes and is obtained in a clear filter over a period of an hour. Ceres takes 9 hours to complete a rotation. These images were made at a sub-solar latitude of -4 degrees and a sub-spacecraft latitude of -26 degrees, revealing a portion of the south pole (down). There appear to be impact craters in the vicinity of the south pole, but the region just to the north appears to be more complex, possibly including ribbon-like structures that might be troughs or ridges extending over many hundreds of kilometers.
Features identified by Hubble (5, 9, 11) are seen above. Extended ribbon-like structures associated with 9 and 11 are noted by arrows, above.
Dawn's encounter with Ceres is the first time the surface (or atmosphere) of a planet has been imaged for the first time by a spacecraft since Voyager 2 flew past Neptune in 1989. Dwarf planets like Ceres and Pluto/Charon (which will be encountered this July by New Horizons) are the most common type of planet in the solar system - and may be the most common type of planet in the universe. Dawn is the first mission to orbit and study such a body in detail to see how it works and compare it to other planets such as Earth. Dawn will be captured by Ceres' gravity on March 6. Dawn will be conducting a series of navigation and rotational characterization observations, each of which will be more exciting than the last. Science operations commence in ernest on April 23 with Rotational Characterization 3 (RC3) at an orbital altitude of 13,500 km (1.3 km/pixel). On June 7, the Survey mapping phase begins at an altitude of 4400 km (and a resolution of ~0.4 km/pixel), then Dawn moves down into its High Altitude Mapping Orbit on August 8 at under 1500 km (140 m/pixel). Finally, Dawn transitions to its Low Altitude Mapping Orbit phase, beginning on December 13 from 375 km (35 m/pixel).
In addition to imaging using the Framing Camera in different filters (operated by the Max Planck Institute for Solar System Research), additional measurements include spectra from a visible and near-IR mapping spectrometer (operated by the Italian INAF-IAPS), and elemental compositional information from the Gamma-Ray Neutron Spectrometer (operated by the Planetary Science Institute). The Dawn mission to Vesta and Ceres is managed by NASA’s Jet Propulsion Laboratory for NASA's Science Mission Directorate.