From
http://apod.nasa.gov/apod/ (Note: this changes every day so that tomorrow it will be different.):
Explanation: What created these bright spots on Ceres? The spots were first noted as the robotic Dawn spacecraft approached Ceres, the largest object in the asteroid belt, in February, with the expectation that the mystery would soon be solved in higher resolution images. However, even after Dawn arrived at Ceres in March, the riddle remained. Surprisingly, although images including the featured composite taken in the last month do resolve many details inside Occator crater, they do not resolve the mystery. Another recent clue is that a faint haze develops over the crater's bright spots. Dawn is scheduled to continue to spiral down toward Ceres and scan the dwarf planet in several new ways that, it is hoped, will determine the chemical composition of the region and finally reveal the nature and history of the spots. In several years, after running out of power, Dawn will continue to orbit Ceres indefinitely, becoming an artificial satellite and an enduring monument to human exploration.
I think that the bright spots are one of two things. Either they are tin cans that held the food that the meteor miners ate, and were dumped here and slagged over by blasters to keep them from floating around on Ceres, and that is why they are so shiny in the sunlight. Or else they are windows to underground Ceres habitats, and the "people" who live in the habitats breathe on the windows now and again, causing the faint haze that mistakenly is thought to be above the windows.
