Alien-hunters have found fresh evidence that Mars was once covered by vast oceans of liquid water. They have proved that a large plain near the Red Planet’s north pole was probably once a martian sea.

The now-dry area closely resembles an ocean basin filled with sediment and it has features just like those of a shoreline. But this seaside strip on Mars is not level which previously led scientists to argue against the presence of an ocean on the site.

Now astrobiologists funded by NASA have shown that the unevenness can be explained by a shifting of Mars’s polar axis. They believe the weight of the ocean itself was enough to move the north pole up to 50 degrees away from where it is today. When the water all disappeared, the paxis shifted back to its current position. Nasa are now likely to pick the spot for future landers.

Carl Pilcher, director of the Nasa Astrobiology Institute in California, said: “This work strongly supports the idea that there were large standing bodies of water on the Martian surface. Interpreting this topography as an ancient northern ocean could have a great impact on current and future Mars exploration.”

Last month, Nasa’s Spirit rover accidentally churned up evidence for past water on Mars. Some European scientists believe that the ancient oceans may have disappeared underground. In December, Nasa reported evidence that water still sometimes flows on Mars.

The picture of Mars’s north pole region was taken from the Mars Odyssey spacecraft.

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