Ancient Martian Oceans Discovered

by ScienceDave | June 14, 2007 at 09:48 am

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Whether little green men were catching sick waves is still under heated debate.

Although it has long been argued oceans on Mars may have existed some 2 billion years ago, there has been a paucity of evidence for ancient oceans on the red planet.

An ocean on Mars would have significant implications for a variety of reasons. First, oceans have a very important role in regulating global climate. Since water can absorb more energy per unit volume than solid ground without changing temperature (referred to as specific heat capacity), it would effectively control the planet's temperature, preventing large variations in temperature (think of a desert).

Second, like on Earth, if ocean currents existed they would help redistribute the bulk of the sun's energy at the equator to the poles, providing a mechanism to make the entire planet more hospitable. For these reasons and others, it has been hypothesized Mars could have supported life forms, if only relatively primitive ones (i.e. single celled organisms, like bacteria)

Two theories have been put forward to explain why oceans DID NOT exist on Mars.

Where are Mars' White Cliff's of Dover?
The first argues that since a certain mineral, calcium cabonate, does not exist in large quantities where Mars' oceans have been proposed to exist, there could not have been any.

One reason why has been the failure to detect significant deposits of carbonates that are associated with the presence of an ocean," Baker said.

When standing bodies of water like Earth's oceans evaporate, the water combines with carbon dioxide in the atmosphere to produce carbonic acid. When that acid interacts with minerals, telltale carbonate deposits are left behind.

However, research completed in 2004, with a little help from the Mars Lander, sheds light on a probable scenario.

NASA's Mars landers and other orbiting spacecraft have recently identified a tremendous abundance of sulfate salts on the red planet. The presence of the salts on Mars was previously unknown to science.

The discovery led Baker and his colleagues to theorize that Mars once featured an ancient ocean sprinkled with sulphates and iron, making the water there just acidic enough to stop carbonates from precipitating.

"This gets us out of [the missing carbonates] dilemma, though in a way that's controversial," Baker said. "It makes for a kind of strange Mars with an acid ocean. But chemically this makes sense for Mars."

Although Baker admits this is not the entire answer, and could very well be incorrect, it does provide a chemical foundation for the lack of carbonates. However, as you will see, there has been a nagging itch on the side of ocean proponents that has been hard to scratch, until now.

Missing Shorelines
The original fodder for Martian oceans originates from images taken of the red planet in the 1970's. There appeared to be shorelines opposite of one another, suggesting the presence of an ancient ocean. However, in 1999 this theory was thought to be put into the grave when these supposed coastlines were shown not be created by water.

The images from Mars Global Surveyor, taken in 1998, have a resolution five to 10 times better than those that Viking provided. With this closer inspection, none of these features appears to have been formed by the action of water in a coastal environment....

..."The newer images do not show any coastal landforms in areas where previous researchers -- working with lower resolution Viking images -- proposed there were shorelines."

Two long shore-like lips of rock in the planet's northern hemisphere were thought to be the best evidence, but experts argued that they were too "hilly" to describe the smooth edges of ancient oceans.

However, recent work from UC Berkely published in the June 14 issue of Nature has reanimated the dead corpse that was once Martian oceans.

Using a simple computer model, they were able to describe how the coastlines that appeared to be too "hilly" became that way. As the planet spins, mass at the equator stays relatively smooth, while away from the equator the landscape tends to bunch up.

"This is the reason why this discovery packs extra punch," Perron said. More than a billion years ago, he explained, something happened in the way mass was distributed on Mars to cause the imbalanced portion to shift toward the equator-and allow the vast shores of the Martian oceans to warp.

"We found evidence of the path the shift would have to have occurred, and it matches with the deformation of the shorelines," Perron said.

Although the exact mechanism for the shift in Mars' mass distribution remains uncertain, Perron does have some ideas to work out.

Perron and his colleagues aren't certain what caused the toppling of the planet, but they think forces beneath the surface are to blame. "There could have been a massive change in the distribution of mantle," Perron said, "which would have caused the planet to shift into its current position."