Quote:Mars once had an enormous ocean covering most of its northern hemisphere, scientists claimed yesterday.

A new map by researchers shows that a network of rivers once flowed from the planet's southern highlands into a massive sea.

The evidence suggests that billions of years ago much of Mars had an "arid continental climate" similar to drier areas of the Earth.

Rain would have fallen regularly and such a wet period would have greatly increased chances of life.

The valley networks are more than twice as extensive as previously thought - and concentrated in a belt around the planet's equator and midsouthern latitudes.

Professor Wei Luo, of Northern Illinois University writing in the Journal of Geophysical Research, said: "All the evidence points to a particular climate on early Mars. It would have included rainfall and an ocean covering most of the northern hemisphere."