NASA is holding a vote on what you think the bright spots on Ceres may be.
Images of Ceres from as far away as the Hubble telescope show a white splotch that everyone assumed would be a crater. Dawn spacecraft images reveal it to be two small, very bright spots inside a crater on an otherwise rather dark dwarf planet.
Dawn entered its first science orbit today, April 24, 2015. Over the next few months Dawn will spiral down to close orbits and we will learn the nature of these bright spots -- but right now all we know is what you can see in the images.
Ceres is expected to contain a lot of ice, though its surface is dark and presumably very dirty. Perhaps a recent impact gouged out a bit of clean ice, underneath the dirt? Or perhaps Ceres has an internal heat source (such as radioactive materials) and can form geysers like those on Enceladus? Or perhaps the white stuff is not ice but salt? Or....