Nasa's Curiosity rover has found evidence that a stream once ran across the surface of Mars.
Evidence for the presence of water on Mars has been found previously, but this evidence - images of rocks containing ancient streambed gravels - is the first of its kind.
The discovery of the rock outcrop which has been named "Hottah" after a lake in Canada's Northwest Territories, came from analysing the size and shapes of pebbles and gravel near the Gale Crater.
At a news conference, Rover project scientist John Grotzinger jokingly said:
The team said it appeared the water was fast-moving and deep.
In this image, a rock outcrop called Link pops out from a Martian surface that is elsewhere blanketed by reddish-brown dust
Scientists say water transport is the only process capable of producing the rounded shape of clasts of this size.
This set of images compares an outcrop of rocks on Mars called Link with similar rocks seen on Earth.
The name Link is derived from a significant rock formation in the Northwest Territories of Canada, where there is also a lake with the same name.
Curiosity is on a two-year mission to investigate whether conditions on Mars could have ever supported microbial life.