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.