Mars’ Northern Hemisphere Shows Signs of Ancient Ocean

BOULDER, Colorado, June 14, 2010 (ENS) – Evidence that an ancient ocean likely covered one-third of the surface of Mars 3.5 billion years ago has been unveiled in a new analysis of satellite imagery conducted by scientists with the University of Colorado at Boulder.

The researchers found evidence in the distribution of ancient martian deltas to indicate there once was an ocean covering the northern hemisphere of Mars.

The 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 idea of a large, ancient ocean on the red planet has been proposed and challenged repeatedly over the past 20 years, the new study provides further support for the idea of a sustained sea on Mars more than three billion years ago, said Gaetano Di Achille, lead author on the study.

Illustration of what Mars might have looked like 3.5 billion years ago when an ocean covered the northern third of the planet (Image courtesy CU-Boulder)

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 the journal “Nature Geoscience.” Both Di Achille and Hynek work with CU-Boulder’s Laboratory for Atmospheric and Space Physics, LASP.

“The climate of early Mars could have supported a complex hydrological system and possibly a northern hemispheric ocean covering up to one-third of the planet’s surface,” write Di Achille and Hynek in “Nature Geoscience.”

“On Earth, deltas and lakes are excellent collectors and preservers of signs of past life,” said Di Achille. “If life ever arose on Mars, deltas may be the key to unlocking Mars’ biological past.”

More than half of the 52 river delta deposits identified by the researchers, each fed by numerous river valleys, likely marked the boundaries of the proposed ocean, since all were at about the same elevation.

Twenty-nine of the 52 deltas were connected either to the ancient Mars ocean or to the groundwater table of the ocean and to several large, adjacent lakes, Di Achille said.

Hynek explained that the study is the first to integrate multiple data sets of deltas, valley networks and topography from NASA and European Space Agency orbiting missions of Mars dating back to 2001.

The study implies that ancient Mars probably had an Earth-like global hydrological cycle, including precipitation, runoff, cloud formation, and ice and groundwater accumulation, Hynek said.

Reconstructed landscape showing the Shalbatana Lake on Mars 3.4 billion years ago. Data used are from NASA and the European Space Agency. (Image by Gaetano Di Achille courtesy CU-Boulder)

The volume of the ancient Mars ocean would have been about 10 times less than current volume of Earth’s oceans, Hynek said. Mars is slightly more than half the size of Earth.

Funded by NASA’s Mars Data Analysis Program, Di Achille and Hynek used a geographic information system, or GIS, to map the Martian terrain.

They concluded that the ocean likely would have covered about 36 percent of the planet and contained about 30 million cubic miles, or 124 million cubic kilometers, of water.

The amount of water in the ancient ocean would have formed the equivalent of an 1,800-foot, or 550-meter deep layer of water spread out over the entire planet.

The average elevation of the deltas on the edges of the proposed ocean was remarkably consistent around the whole planet, said Di Achille.

In addition, the large, ancient lakes upslope from the ancient ocean likely formed inside impact craters and would have been filled by the transport of groundwater between the lakes and the ancient sea, the researchers believe.

A separate study headed by Hynek found roughly 40,000 river valleys on Mars, about four times the number of river valleys that have previously been identified.

Published in the current issue of the American Geophysical Union’s “Journal of Geophysical Research – Planets,” this study involves CU-Boulder researcher Michael Beach of LASP and CU-Boulder doctoral student Monica Hoke.

The river valleys were the source of the sediment that was carried downstream and dumped into the deltas adjacent to the proposed ocean, said Hynek.

“The abundance of these river valleys required a significant amount of precipitation,” he said. “This effectively puts a nail in the coffin regarding the presence of past rainfall on Mars.” Hynek said an ocean was likely required for the sustained precipitation.

Hynek said long-lived oceans may have provided an environment for microbial life to take hold on Mars. Most astrobiologists believe any indications of life on Mars existing now will be found in the form of subterranean microorganisms.

Planetary scientists are interest in the river deltas on Mars because deltas on Earth rapidly bury organic carbon and other biomarkers of life and are a prime target for future exploration.

“One of the main questions we would like to answer is where all of the water on Mars went,” said Di Achille.

He said future Mars missions, including NASA’s $485 million Mars Atmosphere and Volatile Evolution mission, or MAVEN, which is being led by CU-Boulder and is slated to launch in 2013, should help to answer that and other such questions and provide new insights into the history of Martian water.

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