Long suspected and finally discovered: The US probe Mars Odyssey has detected large amounts of frozen water below the surface of our neighbor planet. Measurements of neutrons and gamma rays from the spacecraft launched in April 2001 suggest that ice is hidden in the southern hemisphere of Mars - from the pole to the 60th latitude - to depths of at least 60 centimeters. Its share exceeds 50% by volume - more than half of one cubic meter of Martian soil is therefore in the frozen water. "So you can talk about dirty ice rather than rock with ice, " says William Boynton of the University of Arizona at Tucson, the chief scientist of the gamma-ray spectrometer aboard Mars Odyssey. And this ice is probably only the tip of the iceberg. Because the space probe can not peer deeper into the Martian soil - and not under the winter carbon dioxide ice cap in the northern hemisphere. But if it shrinks in the annual cycle, there may also be more underground water ice detected there. Water on Mars is a popular topic (image of the science 2/2001, "Mars-Gestade"). The possibility that life once existed on the Red Planet - and perhaps still exists today - is given new impetus by the discovery.