Apparently, the lights on Ceres have been a puzzle for a while.
From January 23, 2015:

NASA Finds Mysterious Bright Spot on Dwarf Planet Ceres: What Is It?

A strange, flickering white blotch found on the dwarf planet Ceres by a NASA spacecraft has scientists scratching their heads.

The white spot on Ceres in a series of new photos taken on Jan. 13 by NASA’s Dawn spacecraft, which is rapidly approaching the round dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. But when the initial photo release on Monday (Jan. 19), the Dawn scientists gave no indication of what the white dot might be.

“Yes, we can confirm that it is something on Ceres that reflects more sunlight, but what that is remains a mystery,” Marc Rayman, mission director and chief engineer for the Dawn mission, told space.com in an email.