Intro
Planum Boreum is Mars' massive north polar ice cap, with a diameter of about 1,000 kilometers (600 miles). It consists of four layers: the basal unit, polar layered deposits, a residual ice cap, and a seasonal CO2 ice cap. The basal unit, hidden beneath, is composed of sand and dust cemented by water ice and is over a billion years old. Wind-blown sand from this layer forms extensive dunes around the polar cap. The polar layered deposits hold insights into Mars' climate history and are mostly water ice with layers that suggest varying climate conditions. At the current time, at least, this water-ice cap appears to be in a steady state. It is neither gaining nor losing much each Martian year, and it's periodically covered by a seasonal CO2 ice cap during winter. Come along with us on an expedition across the expansive ice plains of Mars' North Pole. During this journey, you'll have the chance to marvel at distinctive ice formations and explore canyons that cut through the polar cap.
