A frozen crown of water ice, scored by spiraling canyons.
Planum Boreum is the north polar ice cap of Mars, a dome of layered water ice about 1,000 km across and up to 2–3 km thick. It is famous for its dramatic spiral troughs and the vast canyon Chasma Boreale that nearly splits the cap.
Claim your plot here →Planum Boreum is built from countless thin layers of dust and water ice, stacked like the pages of a climate record over millions of years. In winter a meters-thick veneer of frozen carbon dioxide coats the cap, then sublimes away in spring, revealing bright ice beneath. The dome spans about 1,000 km and holds an enormous reservoir of water.
Its most striking feature is a set of dark spiral troughs that swirl outward from the pole, carved and shaped by persistent katabatic winds. A single giant canyon, Chasma Boreale, slices roughly 500 km into the cap, exposing the layered ice like a cliff face and offering scientists a cross-section of Martian climate history.
Comparable in extent to Greenland's ice sheet, but locked at temperatures far below anything on Earth.
The north cap is dominated by water ice, while the southern cap retains a permanent carbon-dioxide ice layer.