These Mars global maps show the likely distribution of water ice buried within the upper 3 feet (1 meter) of the planet's surface and represent the latest data from the Subsurface Water Ice Mapping project, or SWIM. SWIM uses data acquired by science instruments aboard three NASA orbital missions to estimate where ice may be hiding below the surface. Superimposed on the globes are the locations of ice-exposing meteoroid impacts, which provide an independent means to test the mapping results.

The ice-exposing impacts were spotted by the High-Resolution Imaging Science Experiment (HiRISE), a camera aboard NASA's Mars Reconnaissance Orbiter. While other instruments at Mars can only suggest where buried water ice is located, HiRISE's imagery of ice-exposing impacts can confirm where ice is present.

Most of these craters are no more than 33 feet (10 meters) in diameter, although in 2022 HiRISE captured a 492-foot-wide (150-meter-wide) impact crater that revealed a motherlode of ice that had been hiding beneath the surface. This crater is indicated with a circle in the upper-left portion of the right-most globe above.

Scientists can use mapping data like this to decide where the first astronauts on Mars should land: Buried ice will be a vital resource for the first people to set foot on Mars, serving as drinking water and a key ingredient for rocket fuel. It would also be a major scientific target: Astronauts or robots could one day drill ice cores much as scientists do on Earth, uncovering the climate history of Mars and exploring potential habitats (past or present) for microbial life.

The need to look for subsurface ice arises because liquid water isn't stable on the Martian surface: The atmosphere is so thin that water immediately vaporizes. There's plenty of ice at the Martian poles – mostly made of water, although carbon dioxide, or dry ice, can be found as well – but those regions are too cold for astronauts (or robots) to survive for long.

SWIM is led by the Planetary Science Institute in Tucson, Arizona and managed by NASA's Jet Propulsion Laboratory in Southern California. The University of Arizona, in Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., in Boulder, Colorado. JPL, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate in Washington.