Image courtesy MSSS/Caltech/NASA

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NASA's Mars Science Laboratory (aka Curiosity), as seen via self-portraits of its undercarriage.

Image courtesy MSSS/Caltech/NASA

Mars Curiosity Rover Finds Proof of Flowing Water—A First

NASA reveals unprecedented on-the-ground evidence: telltale pebbles and gravel.

NASA's Mars rover Curiosity has made its first major science discovery, and it's one for the ages.

Scientists at the Jet Propulsion Laboratory (JPL) in Pasadena, California, announced Thursday that water—fast-running and relatively deep—once coursed over Mars's now bone-dry surface, a finding based on the presence of rounded pebbles and gravel near the rover's landing site in Gale Crater.

What's more, the researchers estimate that the water was present for thousands to millions of years.

The finding represents the first proof that surface water once ran on Mars. Planetary scientists have hypothesized that the cut canyons and riverlike beds photographed by Mars satellites had been created by running water, but only now do they have on-the-ground confirmation—and the promise of learning much more about the nature and duration of the water flows.

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Author of the National Geographic e-book Mars Landing 2012, Marc Kaufman has been a journalist for more than 35 years, including the past 12 as a science and space writer, foreign correspondent, and editor for the Washington Post. He is also author of First Contact: Scientific Breakthroughs in the Hunt for Life Beyond Earth, published in 2011, and has spoken extensively to crowds across the United States and abroad about astrobiology. He lives outside Washington, D.C., with his wife, Lynn Litterine.