for National Geographic News
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.
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."
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