Martian polar ice caps
The ice-covered regions surrounding Mars’s poles, combining persistent water-ice deposits with seasonal frost composed largely of carbon dioxide.
Carbon dioxide cycle on Mars: The seasonal exchange of carbon dioxide between Mars’s atmosphere and surface frost and ice. Each winter, atmospheric carbon dioxide freezes onto a polar cap; spring sublimation returns much of it to the air.
Water on Mars: Water occurring on Mars as vapor, ice, hydrated minerals, and possibly transient liquid. The permanent polar deposits are Mars’s largest readily visible near-surface water-ice reservoirs.
North polar layered deposits: A thick sequence of ice and dust layers forming the main deposits around Mars’s north pole. These deposits are dominated by water ice and capped by a persistent seasonal and residual carbon-dioxide cover.
Mars Reconnaissance Orbiter: A NASA spacecraft that has orbited Mars since 2006 to study its surface, atmosphere, and subsurface. Its imaging and radar instruments have mapped polar layers and seasonal changes.
Sublimation: The direct transition of a substance from solid to gas without passing through a liquid phase. Polar carbon-dioxide frost disappears mainly by sublimating as sunlight returns.
Water ice: The solid crystalline phase of water, stable on Mars in cold regions and beneath protective cover. It forms the persistent core of both polar ice-cap systems.
South polar layered deposits: A thick sequence of ice and dust layers surrounding Mars’s south pole beneath its residual carbon-dioxide cap. Their water-ice deposits lie beneath a distinctive, enduring cover of carbon dioxide ice.
Shallow Radar: A Mars Reconnaissance Orbiter instrument that uses radar to probe the planet’s subsurface. It detects buried layering and measures the thickness of polar ice deposits.
Martian seasonal frost: A temporary surface coating on Mars, chiefly water or carbon dioxide ice, that forms and recedes with the seasons. This transient frost overlays and expands the polar deposits through the Martian year.
Carbon dioxide ice: The solid phase of carbon dioxide, also known as dry ice. It makes up most seasonal polar frost and part of the southern residual cap.