The study adds to plenty of evidence collected in recent years, most of it by the Mars Global Surveyor, that the Red Planet was once warm and wet.

Scientists have not proved that Mars had oceans, but most leading researchers are convinced that the planet once contained significant amounts of liquid water. Some of that water is now tied up in the polar ice caps, and more may be buried in Martian soil. If there is or ever was life on Mars, water is seen as a key necessity.

Researchers at the University of Arizona, who conducted the new study, billed their findings as the largest flood channels in the solar system, caused by "catastrophic floods of enormous magnitude."

The system of apparent flood channels is 10 times larger than Kasei Valles, the largest previously known outflow channel system on Mars, said University of Arizona researcher James Dohm, who led the new study. Dohm figures they were formed by catastrophic floods that at their peak potentially discharged as much as 50,000 times the flow of the Amazon River.

Dohm and his colleagues, including scientists from NASA Jet Propulsion Laboratory, the U.S. Geological Survey and the Smithsonian Institution, reported the discovery in the June 2001 issue of the Journal of Geophysical Research.

After considering other research into Mars' volcanic past, the researchers say hot magma may have caused the sort of catastrophic floods they think would have carved such huge channels. They suspect several episodes were involved.

Earlier this year, a separate study found evidence that volcanoes may have transported a significant amount of water from underground to the surface of Mars. Other research has shown that some channels on Mars were carved by ice, not water.

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