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© NASAA NASA computer graphic showing concealed glaciers in Mars.
The latest studies have shown Mars once had an enormous ocean in its northern hemisphere that caused a humid and rainy climate like earth.

Scientists from Northern Illinois University (NIU) and the Lunar and Planetary Institute in Houston used an advanced computer program to draw a map of the Red Planet.

"All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars," NIU Geography Professor Wei Luo, said.

The scientists' newly designed map shows the Martian valley networks are more than twice as extensive as had previously been thought.

"It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet's surface," Luo said.

"The presence of more valleys indicates that it most likely rained on ancient Mars, while the global pattern showing this belt of valleys could be explained if there was a big northern ocean," he added.

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