This set of images provided by NASA compares rounded gravel fragments found both on Mars (left) and Earth (right).

NASA/JPL-Caltech/MSSS and PSI

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he image: NASA's Curiosity rover grabbed headlines this week when it delivered strong photographic evidence of "fast-moving and possibly waist-high water that could have possibly supported life" on Mars, says Marc Kaufman at The Washington Post. Specifically, the SUV-sized space lab captured a detailed snapshot of what appears to be an ancient river bed at the base of Aeolis Mons, the 18,000-foot peak in the center of the Gale Crater. (See the full image below, compared to a similar former riverbed on Earth.) "Plenty of papers have been written about channels on Mars with many different hypotheses about what flows in them," says Curiosity science co-investigator William Dietrich of the University of California, Berkeley. "This is the first time we're actually seeing water-transported gravel on Mars." The angular rock outcroppings and rounded shape of the gravel suggest the water flowed for long distances, and may be the strongest evidence yet that Mars was once wet.

The reaction: While it's "too early to tell whether those fast-flowing streams ever housed living organisms," at least now it's "theoretically possible," says Will Oremus at Slate. File this under the "most compelling and detailed evidence" of water on Mars yet. Amd this discovery signals "the real beginning of the rover's science mission," says Sharon Gaudin at Computerworld. Now that scientists are more certain than ever that water flowed on the Red Planet's surface, "they can begin to look for signs of other elements, such as carbon, that are needed to support life." Take a look: