LOS ANGELES - After decades of scouring Mars in search of geologic evidence of past water activity, scientists believe they have found startling evidence that water may even now be flowing through the Red Planet's frigid surface.

This combination of photos released by NASA show two views of a crater in the Centauri Montes region on Mars taken by NASA's Mars Global Surveyor. The image on the right, taken in 2005, shows an area with changes to the surface, suggesting that water occasionally flows on the frigid surface of Mars, raising the tantalizing possibility that the Red Planet is hospitable to life. The image on the left shows the same view of that crater in taken 1999. [AP]

The news excited scientists who hunt for extraterrestrial life. If the finding is confirmed, they say, all the ingredients favorable for life on Mars are in place: liquid water and a stable heat source.

"This is a squirting gun for water on Mars," said Kenneth Edgett, a scientist at San Diego-based Malin Space Science Systems, which operates a camera on NASA's Mars Global Surveyor.

It was the Surveyor that prompted the announcement Wednesday by taking photographs of Mars before it lost contact with Earth last month. The latest findings will appear in Friday's issue of the journal Science.

The images do not actually show flowing water. Rather, they show changes in craters that provide the strongest evidence yet that water coursed through them as recently as several years ago, and is perhaps doing so even now.

In all of its Mars exploration missions, NASA has pursued a "follow the water" strategy to determine if the planet once contained life or could support it now.

Scientists believe ancient Mars was awash with pools of water. And at present-day Mars' north pole, researchers have spotted evidence of water ice. But they have yet to actually see water in liquid form.

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