 The rotation period of Ceres ( the Cererian day ) is 9 hours and 4 minutes . It has a small axial tilt of 4 ° . This is nevertheless large enough for Ceres 's polar regions to contain permanently shadowed craters that are expected to act as cold traps and accumulate water ice over time , similar to the situation on the Moon and Mercury . About 0 @.@ 14 % of water molecules released from the surface are expected to end up in the traps , hopping an average of 3 times before escaping or being trapped . 
