If you know even an inkling of anything about space exploration, you realize that finding flowing water on Mars, our closest planetary neighbor, would be one of the greatest discoveries of the century. The first photographs of Mars, sent back by our probes in the 1960s, showed a dry, desolate planet. But the latest series of images from the wildly successful Mars Global Surveyor (recent Mars missions have been one of NASA’s few bright spots in the last few years) present impressive evidence that non-frozen water has flowed on the Martian surface within the last 5 years:

“Two of those [gullies] originally photographed in 1999 and 2001 then photographed again in 2004 and 2005 showed changes consistent with water having flowed down the side of the crater. “

This is the strongest evidence yet that Mars is not nearly as inactive as we thought. One theory is that there is an underground water source that periodically breaks through to various parts of the surface — not unlike springs and geysers we have here on Earth. Even critics, while urging caution, call the evidence “compelling.”

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