A permanent cap of dry ice over water ice, pocked like swiss cheese.
Planum Australe is the south polar ice cap of Mars, notable for its permanent layer of frozen carbon dioxide sitting atop deep water ice. Its surface is famous for eerie "swiss cheese" terrain — flat-floored pits that grow and shift each Martian year.
Claim your plot here →Unlike its northern twin, Planum Australe keeps a permanent cap of frozen carbon dioxide — dry ice — layered over a much thicker mass of water ice. As sunlight sublimes this dry ice unevenly, it etches the surface into the distinctive "swiss cheese" terrain: rounded, flat-floored depressions that widen year by year, a sign the surface is actively changing.
Beneath the cap lies a vast store of water ice kilometers deep, and radar soundings have hinted, controversially, at possible pockets of subglacial liquid water. Seasonal jets of gas erupt through the ice in spring, flinging dark fans of dust across the frost. Together these make the south pole one of the most dynamic frozen landscapes on Mars.
The south cap keeps a permanent dry-ice layer that the north cap lacks, and it is colder and more pitted.
No place on Earth has a permanent cap of frozen carbon dioxide — this is uniquely Martian.