Water Ice in Korolev Crater

Water ice is permanently stable within Korolev crater because the deepest part of this depression acts as a natural cold trap. The air above the ice cools and is thus heavier compared to the surrounding air. Since air is a poor conductor of heat, the ice is shielded from the surrounding. Only minor warm-up due to heat transfer will happen, and the cold air protects the ice mound effectively from heating and sublimation.