Space scientists have discovered the site of a huge ancient lake on Mars, boosting the chances that the planet has harboured alien life. High-resolution photos from an orbiting spacecraft reveal “unambiguous evidence” for beaches and shorelines, they say.

The lake, which is estimated to be more than three billion years old, is fresh evidence that liquid water once covered the Red Planet. It makes it a prime site for future missions to land on Mars.

The lake appears to have covered up to 80 square miles and been up to 1,500 ft deep. Its bed is located within a much larger valley known as the Shalbatana Vallis.

The lake was identified by researchers from the University of Colorado at Boulder. They found a series of alternating ridges and troughs thought to be surviving remnants of beach deposits along a broad delta.

The team’s leader Gaetano Di Achille said: “This is the first unambiguous evidence of shorelines on the surface of Mars. On Earth, deltas and lakes are excellent collectors and preservers of signs of past life. If life ever arose on Mars, deltas may be the key to unlocking Mars’ biological past.”

Pictures used by the scientists were taken by the most powerful camera sent to another planet, called HiRISE, on NASA’s Mars Reconnaissance Orbiter. It can resolve features on the surface down to one meter in size from its orbit 200 miles above Mars and has found other evidence that water flowed on the planet. Europe’s Mars Express has also spotted strong clues for running water in the past and NASA’s robot rovers have found signs on the surface.

Colorado colleague Assistant Professor Brian Hynek said: “Finding shorelines is a Holy Grail of sorts to us. Not only does this research prove there was a long-lived lake system on Mars, but we can see that the lake formed after the warm, wet period is thought to have dissipated.”

Professor Hynek said Martian lakes would have provided cosy habitats rich in nutrients to feed microbes. In January, NASA revealed that they had detected plumes of methane from Mars which scientists believe may be from simple organisms.

Picture: A reconstruction of the ancient Shalbatana lake on Mars using data from NASA and the European Space Agency. (G. Di Achille, University of Colorado).

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