 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 discoverer 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 . 
 Prior to the Dawn mission , only a few surface features <a href='been_done' title='1'><mark>had</mark></a> 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 discoverer 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 <a href='null_genetive' title='2'><mark>'</mark></a>rotation . Two dark features had circular shapes and <a href='uninflect' title='3'><mark>were</mark></a> 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 <a href='uninflect' title='4'><mark>were</mark></a> then undetermined . One of these features corresponds to the " Piazzi " feature observed earlier . 
Prior to da Dawn mission , only a few surface features done 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 discoverer of Ceres . This was thought to be a crater . Later near @-@ infrared images w a higher resolution taken over a whole rotation with tdaKeck telescope using adaptive optics showed several bright and dark features moving with Ceres  rotation . 2 dark features had circular shapes and was presumed to be craters ; one of them was observed to have a bright central region , whereas anotha was identified as thda Piazzi " feature . Visible @-@ light Hubble Space Telescope images of a full rotation taken in 2003 and 2004 showed eleven recognizable surface features , thedatures of which was then undetermined . One of these features corresponds to the " Piazzi " feature observed earlier .