 Prior to the Dawn mission , only a few surface features had been unambiguously detected on Ceres . High @-@ resolution ultraviolet Hubble Space Telescope images taken in 1995 showed a dark spot on its surface , which was nicknamed " Piazzi " in honor of the <unk> of Ceres . This was thought to be a crater . Later near @-@ infrared images with a higher resolution taken over a whole rotation with the Keck telescope using adaptive optics showed several bright and dark features moving with Ceres ' rotation . Two dark features had circular shapes and were presumed to be craters ; one of them was observed to have a bright central region , whereas another was identified as the " Piazzi " feature . Visible @-@ light Hubble Space Telescope images of a full rotation taken in 2003 and 2004 showed eleven recognizable surface features , the natures of which were then undetermined . One of these features corresponds to the " Piazzi " feature observed earlier . 
