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This ever-icy presence is due to an interesting phenomenon known as a ‘cold trap’, which occurs as the name suggests. The crater’s floor is deep, lying some two kilometres vertically beneath its rim.

The very deepest parts of Korolev crater, those containing ice, act as a natural cold trap: the air moving over the deposit of ice cools down and sinks, creating a layer of cold air that sits directly above the ice itself.

Behaving as a shield, this layer helps the ice remain stable and stops it from heating up and disappearing. Air is a poor conductor of heat, exacerbating this effect and keeping Korolev crater permanently icy.