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New radar measurements from the European probe Mars Express indicate that Mars’ southern polar cap contains enough water ice to cover the entire planet in 36 feet (11 meters) of water. Jeffrey Plaut of NASA’s Jet Propulsion Laboratory led the study, published in the March 15 issue of the journal Science.

Lower ground is purple and blue, higher orange and red, on this topographic map of Mars’ south polar cap. The ice layer probed by Mars Express’ radar is outlined in black; the solid black area is out of Mars Express’ range. (NASA/MOLA Science Team)

Mars Express used its radar instrument to probe the ice. It shined a beam of radio waves down to the surface, which penetrated the ice to the rock beneath and reflected back to the spacecraft. The measured round-trip time allowed scientists to calculate the ice’s depth.

“The south polar layered deposits of Mars cover an area as wide as a big portion of Europe,” Plaut said. “The amount of water they contain has been estimated before, but never with the level of confidence that this radar makes possible.”

The radar instrument has made more than 300 “virtual slices” through the south polar cap of Mars. It has found that, in some spots, the ice is up to 2.3 miles (3.7 km) deep.

Though evidence shows that much of the Red Planet was covered in water in the past, today Mars’ polar caps contain most of the planet’s water.

Mars Express continues to map the planet’s northern polar cap with radar. — Rebecca Johnson