An ancient waterway in the southern highlands of Mars breaks through the wall of a giant crater, flooding a huge lake with water and clay minerals.

The spread of deposits across the base of the 25-mile-wide Jezero crater shows that extensive water must have persisted in the lakebed for thousands of years, suggesting the planet was once host to vast lakes and flowing rivers that could perhaps have supported life. "The big surprise from these new results is how pervasive and long-lasting Mars' water was," said Scott Murchie at Johns Hopkins University in Maryland.

The image, published in Nature and Nature Geosciences, is among several taken recently by a camera on Nasa's Mars Reconnaissance Orbiter. The maps will help Nasa officials decide on landing sites for future missions, including the Mars Science Laboratory, due to launch late next year. "If life ever existed in this region, there's a chance of its chemistry being preserved in the delta," said Bethany Ehlmann at Brown Univeristy in Rhode Island.

The clay-like minerals preserve a record of between 4.6bn and 3.8bn years ago, the earliest years of the solar system, when the Earth and Mars sustained a cosmic bombardment by comets and asteroids. "In a few locations a great deal of water must have flushed though the rocks and soil," said John Mustard, a co-author at Brown University. "We're finding dozens of sites where future missions can land to understand if Mars was ever habitable and if so, to look for signs of past life."

What the colours mean

Scientists say this proves water flowed freely on Mars between 4.6bn to 3bn years ago. The colours come from an instrument on the Mars Reconnaissance Orbiter satellite looking for water: the Compact Reconnaissance Imaging Spectrometer for Mars. CRISM takes a picture of all kinds of light, from visible to infrared and ultraviolet. The images (taken in strips 10,800 metres wide) allow scientists to work out what the surface of Mars is made of.