Free Astronomy Magazine July-August 2015

PLANETOLOGY emerged from underground. But this cra- ter could also have been originated by the impact of a small asteroid and con- sequently it was necessary to wait for successive images with higher resolution before attempting fur- ther interpretations. However, the wait was not long, given that on 6 March the spacecraft would have began its manoeuvres for entering into orbit around Ceres; an opera- tion that Dawn completed success- fully, making it first spacecraft to orbit two different extraterrestrial planetary bodies. The approach tra- jectory to the dwarf planet caused the spacecraft to be, scientifically, of little use for over a month, both because Dawn’s momentum car- ried it to the altitude of 75,400 km (on 18 March), and because it tran- sited in the shadowed hemisphere of Ceres. As it continued its path towards the lighted hemisphere, the space- craft gradually moved on a trajec- tory closer to Ceres, and on 23 April it reached an altitude of 13,500 km, into the first planned scientific orbit. This phase, needed for an initial surface mapping, end- ed on 9 May, when Dawn reignited its in- novative ion engine and began a month- L eft, one of the first shots taken on 6 May during the second mapping phase at a distance of 4,400 km. In the foreground a large crater of the south- ern hemisphere, with many struc- tures which can be associated with meteorite impacts (410 mt/pixel reso- lution). [NASA/JPL- Caltech/UCLA/MPS/ DLR/IDA] Below, a portion of the north- ern hemisphere of Ceres, taken in the visible, near-infra- red and thermal- infrared range. [NASA/JPL-Caltech/ UCLA/ASI/INAF]