Two studies in the past year have supported the idea that large amounts of water once existed on Mars, likely flowing to the surface in large violent bursts to carve deep channels in catastrophic floods.

Some of the evidence suggests that water may still reach the surface.

But a longstanding question remains: Where did the water come from?

New evidence indicates that much of the water may have been hauled to the surface by hot lava released during volcanic eruptions.

Clues are found in more than a dozen Mars rocks that have been found on Earth. These meteorites were ejected from the Red Planet, probably after an asteroid or comet collision, and traveled here. Past studies of these rocks have found little evidence for water.

But in the new study of a meteorite named Shergotty, ejected from Mars 175 million years ago and found in India in 1865, researchers found crystallized minerals called pyroxenes. These could only be present if the 11-pound (5-kilogram) rock contained water before it reached the surface of Mars, according to University of Tennessee geologist Harry McSween Jr. and his colleagues.

The researchers say Shergotty, thought to be a volcanic rock, held 1.8 percent water before it reached the Martian surface.

The finding, which appears in the Jan. 25 issue of the journal Nature, does not explain how water got to Mars in the first place.

Towering volcanoes on the Martian surface attest to a violent past. Researchers don't know if volcanic activity continues today, but many suspect it might. If so, here's how they say water would get to the surface: Hot molten rock, called magma, is generated deep down. It rises until it meets cooler rocks that contain hydrogen-bearing minerals. These minerals decompose when heated by the magma and the hydrogen is released, dissolving in the magma and forming water.

The magma continues toward the surface, where it erupts from a volcano and its water is released in the form of vapor. Think of the bubbles escaping a soda when you open the bottle.

Scientists say water from Earth's interior reaches the surface in a similar fashion.

Massachusetts Institute of Technology researcher Timothy Grove, working with McSween, makes fake Mars rocks in his laboratory. By subjecting these synthetic rocks to high temperatures and pressures, he can figure out how much water would be contained in magmas at the time their crystals formed.

"What my experiment can do is estimate how much water was involved in the process that led to the formation of Mars meteorites," Grove said. "The only way you can reproduce the unique chemical composition of these minerals is to have water present."

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