What is the name of Mars’s northern polar ice-cap region?

Mars’s northern polar ice-cap region is called Planum Boreum. The name comes from the Latin word for northern and the Roman name for the north wind. It is a broad, elevated plain surrounding Mars’s north polar cap.

Planum Boreum contains layered deposits of water ice and dust. These layers record changes in the Martian climate over long periods, somewhat like ice layers in terrestrial polar regions. During winter, carbon dioxide frost adds a seasonal coating to the permanent water-ice deposits.

The region includes Chasma Boreale, a vast canyon that cuts into the polar layered deposits. Mars’s southern polar region is instead called Planum Australe, a common source of confusion. The two polar caps also behave differently because Mars’s seasons and orbital geometry create distinct patterns of seasonal carbon-dioxide frost.

Spacecraft including Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter have mapped Planum Boreum in detail.