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The Red Planet was once blue... Giant ocean once covered third of Mars
By Daily Mail Reporter
Last updated at 8:42 AM on 24th November 2009
[size=1.2em]A vast ocean once covered a third of Mars, scientists believe.
[size=1.2em]Such a stunning prospect greatly increases the chances of life having existed on the Red Planet, the fourth from the Sun in our solar system.
[size=1.2em]Researchers have come to the conclusion after using new software to analyse images of the surface. As a result, they have managed to find dozens of valleys to build up the most detailed map to date.
The areas marked in red show where scientists believe valleys were caused by a network of rivers feeding into the ocean. This area is twice that mapped by earlier research, right
The area in blue shows where the ocean would have been. The yellow, red and green belt below it is where scientists found the valleys. They believe these were caused by water running from the south towards the ocean in the north
[size=1.2em]The valleys, first spotted in 1971, were caused by a network of rivers more than twice as extensive as previously mapped. The water channels were in a belt between the equator and mid-southern latitudes.[size=1.2em]
[size=1.2em]The experts from Northern Illinois University and Nasa believe they mark the paths of rivers that once flowed from the planet's southern highlands into a huge ocean in the north.
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[size=1.2em]The evidence suggests that billions of years ago much of Mars had an 'arid continental climate' similar to drier areas of the Earth.[size=1.2em]
[size=1.2em]Rain would have fallen regularly, swelling the rivers and topping up the ocean basin. Such a wet period early in the planet's history would have greatly increased the chances of life.[size=1.2em]
[size=1.2em]Until now the only global map of Martian valley networks that existed was incomplete and drawn by hand from satellite images.
Mars today: Nasa's Exploration Rover Spirit recorded this view of the Red Planet's dusty surface in October of this year
 Writers and artists once thought Mars could be a lush planet with a population of Martians. The pictures beamed back from Viking 1 in 1976 quickly dispelled this view.
[size=1.2em]This indicated that valley networks are far more sparse on Mars than on Earth, raising doubts that they were created by the 'run-off erosion' of rivers.[size=1.2em]
[size=1.2em]An alternative explanation, known as 'groundwater sapping', was that water springing or seeping out of the ground eroded the channels.[size=1.2em]
[size=1.2em]The new map, created by a computerised analysis of satellite data, shows that some regions of Mars had valley networks almost as dense as those on Earth.[size=1.2em]
[size=1.2em]'It is now difficult to argue against run-off erosion as the major mechanism of Martian valley networks,' said research leader Professor Wei Luo, from Northern Illinois University.[size=1.2em]
[size=1.2em]The belt pattern of the valley network could best be explained if there was a large northern ocean, said the scientists writing in the Journal of Geophysical Research - Planets.[size=1.2em]
[size=1.2em]The Martian surface is characterised by lowlands located mostly in the northern hemisphere, and highlands mostly in the planet's southern half.[size=1.2em]
[size=1.2em]A planet-wide ocean may once have covered the northern regions where the lowlands exist today, the scientists believe.[size=1.2em]
[size=1.2em]The features resembling dry river valleys on Mars have been hotly debated by scientists since their discovery by the Mariner 9 spacecraft in 1971.[size=1.2em]
[size=1.2em]But, according to the US researchers, the extent of the valley networks has been greatly underestimated until now.[size=1.2em]
[size=1.2em]Professor Luo added: 'A single ocean in the northern hemisphere would explain why there is a southern limit to the presence of valley networks.[size=1.2em]
[size=1.2em]'The southernmost regions of Mars, located farthest from the water reservoir, would get little rainfall and would develop no valleys. This would also explain why the valleys become shallower as you go from north to south, which is the case.'[size=1.2em]
[size=1.2em]The Mars of today is a bitter cold place and bone dry, the rivers and seas are long gone. Its atmosphere is thin and wispy, and if microbes still exist, they're probably eking out a meagre existence somewhere beneath the planet's dusty soil.
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发表于 2009-11-26 09:45
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