That's one big ice rink.
Some 51 miles (82 kilometers) across, the Korolev crater is located in the northern lowlands of Mars, just south of a large patch of dune-filled terrain that encircles part of the planet's northern polar cap. The crater is filled with ice, not snow, and its center features a mound of water ice that's about 1.24 miles (2 kilometers) thick year round.
It turns out that this crater is a winter wonderland all year. The deepest parts of this crater contain ice, and this creates a natural cold trap around the crater. The air moving around this ice cools down and sinks, resulting in a layer of cold air that sits just over the ice itself. It acts like a shield, keeping the ice stable and preventing any warmer air from melting it.
The images you see here are actually compilations of five different "strips" that were edited together. Each strip was captured during a different orbit by the European Space Agency's Mars Express spacecraft. Launched in June 2003, Mars Express entered the red planet's orbit on Dec. 25, 2003, making these icy pictures an appropriate 15th anniversary gift.
Martian ice is kind of like crystal, the traditional 15-year anniversary gift, right? Well, in this case, close enough.