Free Astronomy Magazine July-August 2015

L eft, a shot of Ceres taken on 5-6 May at a dis- tance of 13,600 km. The two bright spots at the bottom of a crater were al- ready very evi- dent. Below, the enigmatic struc- ture photogra- phed in detail on 6 June. The main spot is located right in the centre of the crater, and it is about 13 km across. In the video on the left we can see Ceres as viewed by Dawn at varying heights ranging from 13,600 km to 5,100 km. [NASA/JPL-Cal- tech/UCLA/MPS/ DLR/IDA] PLANETOLOGY While waiting to know the composition and origin of those bright deposits, it is al- ready possible to attempt a rough comparison between the surfaces of Ceres and Ves- ta, because if it is true that they have a lot in common, like the abundance of craters, it is also true that Ceres ap- pears to have had a greater surface activity, as evidenced by various areas affected by landslides, streams of once fluid materials, and structural col- lapses. After having orbited seven times around Ceres at an altitude of 4,400 km, collecting among other things valuable geological and spectrometric information, including the infrared, on 28 June Dawn reignited its ion engine and began to descend again towards a smaller orbit, which by early Au- gust will take it to an altitude of just 1,450 km. We will surely have the opportunity to return to this subject in the future. n of images useful for its correct navigation, in which a resolution of 480 mt/pixel had been reached. These and other excellent images taken subsequently have allowed to confirm that the two groups of bright spots are the most reflective structures of the en- tire globe and that they are constituted by many smaller individual spots of different shapes and sizes, with an increased concen- tration towards the centre of the two group- ings. In commenting these structures, Rus- sell said: “The bright spots in this configu- ration make Ceres unique from anything we’ve seen before in the solar system. The science team is working to understand their source. Reflection from ice is the leading candidate in my mind, but the team contin- ues to consider alternate possibilities, such as salt. With closer views from the new orbit and multiple view angles, we soon will be better able to determine the nature of this enigmatic phenomenon” .