US satellite observations have produced the first strong evidence for water flowing on Mars. 

The water is a brine saturated in salts such as perchlorates. As it seeps down the slopes of Martian craters and mountains, it leaves narrow streaks less than five metres wide, which appear and lengthen during the warm season and fade during the Martian winter. 

Although the salty liquid would not be drinkable by visiting astronauts in its present form, the presence of any water strengthens the idea that Mars may harbour microscopic lifeforms. 

“Our quest on Mars has been to ‘follow the water’ in our search for life in the universe, and now we have convincing science that validates what we’ve long suspected,” said John Grunsfeld, Nasa’s head of science. “This is a significant development, as it appears to confirm that water, albeit briny, is flowing today on the surface of Mars.”

Nasa scientists announced their “major science finding” at a news conference in Washington and in a scientific paper published in the journal Nature Geoscience.