Water was running freely on Mars about one million years ago, according to new pictures from the planet.
Images from a Nasa spacecraft orbiting the Red Planet show fan-shaped gullies on the surface which seem to be about 1.25 million years old.
Experts think the channels were created by surface water from melting ice.
The team from Brown University, in Rhode Island, America, say it may represent the most recent time when water flowed on the planet.
But Samuel Schon, from the university, said that didn't mean there was a lot of water about, adding: "You never end up with a pond that you can put goldfish in."
But he said signs of a gully system for the water, even though it dates back to more than one million years ago, did add to evidence that Mars experienced an ice age.