Mercury is very close to the Sun. Yet, recent evidence shows that Mercury has polar ice caps. To have ice caps, water ice must be present. When Mercury was formed, its water evaporated. Mercury may have gotten water ice from comets when they collided with the planet. If the collision took place on the dark side of the planet, the water ice would remain frozen. The temperature falls well below freezing during the long night.
During the day, the water ice needs to be protected from evaporation. With no atmosphere to spread heat around, areas in shade remain cold. To keep from evaporating, the ice would have to
