The newest U.S. spacecraft to orbit Mars, the Odyssey, has discovered vast amounts of water on the red planet during its first week of observations. The discovery supports the notion that life might have existed there at one time.

The Mars Odyssey, launched last April, has detected what scientists believe is a large amount of water in the form of ice at the Martian south pole covering a surface area more than 600 kilometers across.

Scientists have long known of the presence of water on Mars, but University of Arizona astronomer William Boynton says the new results go beyond the volume expected. "The signal that we've been getting loud[ly] and clear[ly] is that there is a lot of ice on Mars. We've seen really a lot of ice in the southern hemisphere all the way from the south pole on up to about -60 degrees latitude," Mr. Boynton explains.

Mr. Boynton has said further observations are required to determine the precise extent of the ice, but he suggests it amounts to a significant percentage of the planet's surface, mostly mixed in with the top meter of soil. "We really are excited about seeing that," he says.

U.S. space agency Odyssey project scientist Stephen Saunders explains why all the excitement. "Water is vital to life. Water has changed the face of Mars in the past. And water is necessary for the future exploration of Mars," he says.

The spacecraft detected the Martian water indirectly, by sensing significant amounts of hydrogen, a component of water.

William Boynton says his team judged it to be hydrogen based on the characteristic intensity and wavelength of gamma rays emitted from it when displaced by the natural bombardment of atomic particles called neutrons.

"One of the reasons we feel very comfortable coming up with this conclusion, even after looking at the data for only about a week, because we've also seen it by other instruments as well," Boynton says.

Mr. Boynton says a similar amount of water might also exists at Mars' north pole hidden under a layer of carbon dioxide ice. It might be revealed by the thaw as the north emerges shortly from winter.

Odyssey's camera system is also studying Mar's surface minerals to reveal the red planet's geologic history. Arizona State University astronomer Phillip Christensen says an infrared camera is measuring differences in heat emissions between soil and rocks, helping map the composition of the terrain 30 times sharper than instruments on previous spacecraft at Mars.

"This will tell us a great deal about the physical state of Mars, where rocks are, where erosion has occurred. We can't see these rocks, but we know they are there from their temperature signature. It truly provides a whole new way of looking at the planet," he says.

Other measurements made as Odyssey was enroute to Mars suggests that the daily dose of radiation astronauts would get on a voyage there would be more than twice the amount experienced aboard the international space station. A subsequent failure of the instrument to communicate has foiled efforts to measure radiation hitting Mars' surface.