One image captured by the Mars Express spacecraft, sent by the European Space Agency, shows an extraordinary valley on Mars, which might be a landing site for ExoMars 2020.

This is one of Mars' biggest valleys. Scientists confirm that the region might have been habitable 3.6 billion years ago. There seem to be signs of a large quantity of water in this region, starting at a higher plane and then falling into the northern plains.

Mawrth Vallis is located between southern highlands and the northern lowlands, according to the Esa. There seem to be some "light-toned structures" that hint of signs of water in some past era. The 205,000 square miles around Mawrth Vallis disclose that water shapes its surface.

Another interesting find is that of volcanic ash like a dark cap rock here, which probably contain faint traces of ancient microbes. There are light-toned phyllosilicates along its course, which indicate water, with the possibility that the environment was once habitable.

Scientists collected nine photos shot by the Express spacecraft's high-resolution camera and created an image. They found that the Red Planet might have been crisscrossed with networks of lakes and streams for a billion years more than imagined earlier. Nasa researchers made the discovery by dating 22 impact craters on the planet.

"We discovered valleys that carried water into lake basins," said Sharon Wilson from the Smithsonian Institution in Washington.

"Several lake basins filled and overflowed, indicating there was a considerable amount of water on the landscape during this time."

Wilson and colleagues examined the features of images from cameras on the Mars Reconnaissance Orbiter, Nasa's Mars Global Surveyor and the European Space Agency's Mars Express.

"One of the lakes in this region was comparable in volume to Lake Tahoe," Wilson said. "This particular Martian lake was fed by an inlet valley on its southern edge and overflowed along its northern margin, carrying water downstream into a very large, water-filled basin we nicknamed "Heart Lake".'

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