Mars Had Ocean, Controversial New Theory Says

Brian Handwerk
for National Geographic News
September 22, 2004
Did Mars have an ocean or didn't? Mounting evidence suggests the red planet may have featured oceans or other large bodies of water in the past. But the theory also raises a nagging question.

"We have evidence of huge amounts of water, and a segment of the scientific community has been convinced that Mars had oceans since at least the 1980s," said Victor Baker, a planetary scientist and geoscientist at the University of Arizona in Tucson.

But other scientists disagree. "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.

The Martian atmosphere is rich in carbon dioxide. Yet spectral imaging has shown only small amounts of carbonates scattered across the planet's dusty surface.

So why aren't there more carbonates on Mars if the planet had oceans long ago?

A recent study by Baker and other researchers, published in tomorrow's issue of the science journal Nature, offers a controversial theory that potentially solves the dilemma.

Acid Ocean

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."

Mars has been volcanically active throughout its past up to modern times, Baker said. Eruptions and other volcanic activity "release iron and sulfur dioxide that can produce these types of acidic conditions," he said.

Baker and his colleagues say they've only spawned the beginning of an idea that will hopefully lead scientists to a fuller understanding of the red planet's past.

The new study suggests what is physically reasonable. But it does not attempt to test the theory through the long history of Mars. Scrutiny of such a vast geologic record has yet to be attempted.

"Our feeling is that, like all science, this may not be the absolute correct answer. But it can stimulate work that can get us there," Baker said. "It's consistent with the data … [and implies] that we're at least following the right path."

The theory lends its controversial weight to gathering evidence that suggests ancient oceans existed on Mars. Oceans are considered a key criteria for past life on Mars.

NASA's Mars exploration rover Opportunity has identified perhaps the best evidence for water on the red planet from its landing zone in the Meridiani Planum, a flat area near the equator.

Rocks on that plain yielded clues of texture, mineral composition, and chemistry that strongly suggest that the geologic matter was deposited in flowing, salty water.

"The plains themselves extend over an area about the size of Oklahoma," said Joy Crisp, a Mars Exploration Rover Mission scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

"We have seen roughly 30 feet [10 meters] of thickness of these [deposited] layers, laid down one after the other," she said. "So we're getting a sense that this body of water was around for some time."

Data collected in orbit suggest the sediment stack was some 1,650 feet (500 meters) thick and covered an area the size of Northern Europe's Baltic Sea.

Had it existed, might such a vast, ancient sea once have teemed with life? No one knows for sure. But the authors of the new study suggest that the acidic nature of the Martian ocean they say existed might have been suitable for life.

Writing in their study, the researchers stated: "In fact, if biological inhabitation of early Mars is considered plausible, moderate acidic oceans represent the closest terrestrial analogue for a biogenic environment, similar to that where life originated on … Earth."

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