Scientists report new signs of water on Mars

For decades, space scientists have searched Mars for signs of water, the liquid generally believed to be essential for life. Now, they may well have found it.

Scientists announced yesterday that they had detected dozens of slopes across the southern hemisphere of the planet where previously undetected dark streaks come and go with the seasons. When the planet heats up, the streaks appear and expand downhill. When it gets cold, the streaks disappear.

The best explanation they have so far is that those dark fingerlike streaks are a kind of salty water that is running on or just below the Martian surface. At one location - Newton Crater - they have counted as many as 1,000 of these possible streams flowing down the slopes and into a basin.

It's a discovery that, if confirmed, would fundamentally change our understanding of Mars and would strongly support the widely held theory that the planet was once far more wet and warm. And scientists say the discovery of water would provide our best target yet for finding possible life beyond Earth.

"We haven't found any good way to explain what we're seeing without water," said Alfred McEwan of the University of Arizona's Lunar and Planetary Laboratory. He's the lead author on a paper about the possible Martian water in the journal Science.

"And if we confirm that it is a salty water, then we have the best idea yet about where to go to try to find extant life on Mars," McEwan said.

The "dark streaks" were initially noticed by a student at the school in images sent back by the Mars Reconnaissance Orbiter.

The pixelated images were taken as far back as 2007, but with so much data coming in from space missions, they had remained unstudied. McEwan suggested that the student - geophysics junior Lujendra Ojha - examine over time the locations with streaks, and Ojha found that the streaks changed dramatically by season.

"None of these images by themselves are particularly revealing," McEwan said. "But when you put them together and see what happens over time, then you can clearly see something important is happening."