CU: An ancient ocean may have covered one-third of Mars

[bystander]

New CU-Boulder study indicates an ancient ocean may have covered one-third of Mars
University of Colorado at Boulder via EurekAlert - 13 June 2010

Martian ocean likely sustained by Earth-like hydrological cycle

A vast ocean likely covered one-third of the surface of Mars some 3.5 billion years ago, according to a new study conducted by University of Colorado at Boulder scientists.

The CU-Boulder study is the first to combine the analysis of water-related features including scores of delta deposits and thousands of river valleys to test for the occurrence of an ocean sustained by a global hydrosphere on early Mars. While the notion of a large, ancient ocean on Mars has been repeatedly proposed and challenged over the past two decades, the new study provides further support for the idea of a sustained sea on the Red Planet during the Noachian era more than 3 billion years ago, said CU-Boulder researcher Gaetano Di Achille, lead author on the study.

A paper on the subject authored by Di Achille and CU-Boulder Assistant Professor Brian Hynek of the geological sciences department appears in the June 13 issue of Nature Geoscience. Both Di Achille and Hynek are affiliated with CU-Boulder's Laboratory for Atmospheric and Space Physics.

Did a Deep Sea Once Cover Mars?
Science NOW - 13 June 2010

Once upon a time, a deep ocean covered one-third of Mars. Then, billions of years ago, it dried up, leaving the arid, rocky planet we see today. It's a provocative idea, but is it true? In a new study, researchers argue that it is, pointing to river deltas that, they say, mark the ancient sea level. But experts say the new evidence still isn't enough to carry the day.

Proving that 100 million cubic kilometers of water once filled the martian lowlands is a lot harder than it might seem. The putative sea floor was long ago covered by lava, and faulting and erosion have muddled any lingering shoreline along the lowland-highland boundary. So Gaetano Di Achille and Brian Hynek of the University of Colorado, Boulder, considered 52 martian deltas—piles of river-borne sediment—that formed at the level of some body of standing water, as the Mississippi delta is forming at the level of the Gulf of Mexico.

As the pair reports today in Nature Geoscience, 17 of the 52 deltas formed either on the edge of the lowlands or on basins or huge channels that open into the lowlands. And although the 17 are spread around the planet, they are at the same elevation plus or minus 177 meters (one standard deviation). The simplest explanation, they say, is that all of these deltas formed around the same ocean about 3.5 billion years ago, when Mars is thought to have been at least somewhat wetter and warmer than it is now. The level of the deltas is also generally consistent with "large portions" of a previously claimed shoreline as well as with the locations and terminations of ancient martian valley networks.

River deltas hint at ancient Martian ocean
Nature News - 13 June 2010

Similar heights of channel mouths suggest they fed into one body of water.

Planetary geologists in the United States have analysed data that suggest Mars was once home to a huge ocean of water, covering nearly one-third of its surface. Their evidence, a ring of dry river deltas and valleys all at a similar elevation, adds weight to the idea that the red planet once supported an Earth-like water cycle.

Hints that an ocean once occupied the northern lowlands of ancient Mars first arose in the late 1980s. Scientists examining pictures of the surface claimed to recognize extensive shorelines and vast networks of river valleys and outflow channels feeding in the same direction. Other researchers used thermal physics to imply that such networks could only have been carved by a complete water cycle, fuelled by one or more huge bodies of water.

Not all evidence has supported the idea of a Martian ocean, however. In the late 1990s, researchers studying high-resolution images of the proposed shoreline regions could not find any of the erosion and sediment normally associated with an ocean's edge. Nor have they since found the telltale coastal landforms seen on Earth, such as spits and wave-deposited ridges.

Gaetano Di Achille and Brian Hynek of the University of Colorado in Boulder, whose study could now tip the balance back in favour of an ancient ocean, initially had no interest in the debate. They had been building a database of Martian river deltas and valleys to examine how they might have been eroded by water, but ultimately realized that they had enough data to tackle the bigger picture. "Our research started as kind of a joke," says Di Achille. "We were working on this database of deltas and valleys, and we said: why don't we try to check this ocean hypothesis?"

Ancient ocean on Mars supported by global distribution of deltas and valleys

• Nature Geoscience | 13 June 2010 | doi: 10.1038/ngeo891

Ancient Mars Covered by Vast Ocean
Space.com - 13 June 2010

More than 3 billion years ago, the northern plains of Mars were covered by a vast ocean that blanketed more than a third of the red planet's surface, new research suggests.

Previous spacecraft investigations have pointed to possible signs of an ancient ocean on Mars. Still, this idea has been challenged for decades, as past evidence has been uncertain, and the matter remains one of the greatest open questions when it comes to researching the red planet.

Now scientists have analyzed global databases of river valley networks on Mars, as well as deposits left behind by ancient deltas. Their research suggests 29 deltas they investigated -- more than half of all those in the databases -- sat at roughly the same height some 3.5 billion years ago, apparently ringing a vast ancient ocean shoreline in the northern lowlands of Mars.

• 
  Reconstruction of the possible Martian ocean that may have covered one third of the planet about 3 billion years ago.
  What the Ocean Looked Like (B. Hynek / Nature Geoscience)

"Our findings lend credence to the existing theories regarding extent and formation time of an ancient ocean on Mars," said researcher Gaetano Di Achille, a planetary geologist at the University of Colorado at Boulder. "Moreover our test suggests that early Mars could have likely had a global water cycle similar to the present hydrological configuration of our planet."

[Ann]

Mars may have abundant water in the past, but if it did the water is all gone now, at least all the liquid water. To me, the most important lesson here is that while Mars may have had an ocean three billion years ago, the Earth has had an ocean for more than three billion years, and it is still there. We should definitely be more amazed at the Earth than we are at Mars.

Ann

[bystander]

Ocean once covered the northern third of Mars
ars technica - 15 June 2010

• 
  G. Di Achille

There's little doubt that, at least early in its history, Mars had significant quantities of liquid water. Everything from mineral deposits to ancient shorelines and river-like features indicate that the watery period peaked near the border between the planet's Noachian and Hesperian epochs, about 3.5 billion years ago. There has been some debate, however, about just how much water was present at that time. A paper published over the weekend in Nature Geoscience argues that there was enough to cover the planet's northern pole in an ocean.

The logic of the analysis is pretty simple, and applies the sort of reasoning we use for determining the Earth's historic ocean levels. In short, you look for geologic features indicative of a shoreline, and see if they line up at the same altitude. In this case, the two authors used a database that tracks the appearance of river deltas on the Martian surface, and uses the Mars Observer Laser Altimeter dataset to get elevations for each of them. If an ancient ocean existed, these features should exist within a narrow range.

On a first pass, the data didn't look very promising, as the mean elevation of the 52 deltaic deposits under consideration varied widely (the standard deviation was over a kilometer). But the authors went through and analyzed each deposit individually, and found that many were associated with a local basin, such as a large crater. Only a third of the features were associated with the outflow of water into the basin that covers the northern hemisphere of the planet, and these were tightly clustered in elevation (a mean elevation of of -2,540m with a standard deviation of 177m).

The authors point out that this is exactly what you'd see if you were looking at an ancient shoreline, writing, "Therefore, the deposits topographically connected to the site occupied by the putative ocean define the closest approximation of an equipotential surface as would be expected if they formed in a single large body of standing water encompassing the northern hemisphere of Mars."

Data from outside the region suggests that there might have been a planet-wide water table in the crust, as there are almost no valleys below the shoreline level that date from the Noachian, even in areas well removed from the northern basin. That changes in more recent eras, suggesting a gradual loss of water planet-wide.

Cumulatively, there seems to have been a lot of water involved—the authors estimate that over 108 cubic kilometers may have been present, with 36 percent of the planet's surface covered in water.

Nature Geoscience, 2010. DOI: 10.1038/NGEO891

[Ann]

Definitely interesting.

I find it remarkable, however, that a planet which ought to have been considerably colder than the Earth had one of its polar regions covered in liquid water. Any thoughts?

Ann