Was Mars covered with water?

Image of Mars from orbit

Some scientists think that Mars had a huge ocean billions of years ago.

  • Thousands of river valleys on Mars
  • Millions of cubic km of water
  • Probably covered 36% of the planet

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 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 water system on early Mars.

The notion of a large, ancient ocean on Mars has been repeatedly proposed and challenged over the past two decades.

But 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.

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

Illustration of what Mars might have looked like

Illustration of what Mars might have looked like some 3.5 billion years ago when an ocean might have covered one-third of the planet's surface.

Twenty-nine of the 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.

124 million cubic km of water

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

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

Di Achille and Hynek conclude the ocean likely would have covered about 36 percent of the planet and contained about 30 million cubic miles, or 124 million cubic kilometres, of water.

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

This is about 10 times less than current volume of Earth’s oceans, Hynek said. Mars is slightly more than half the size of Earth.

A dry river valley on Mars

Scientists have catalogued 40,000 dry river valleys on Mars.

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, according to the researchers.

40,000 Red Planet rivers

A second study headed by Hynek and involving other CU-Boulder researchers, detected roughly 40,000 river valleys on Mars. That’s about four times the number of river valleys that have previously been identified by scientists, said Hynek.

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.

“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 US$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 such questions and provide new insights into the history of Martian water.

The river deltas on Mars are of high interest to planetary scientists because deltas on Earth rapidly bury organic carbon and other biomarkers of life and are a prime target for future exploration.

Most astrobiologists believe any present indications of life on Mars will be discovered in the form of underground micro-organisms.

“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.”

Adapted from information issued by University of Colorado at Boulder / NASA /Malin Space Science Systems / MGS / JPL.

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