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20 percent of Mars' surface was likely water 4.5 billion years ago

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The body of water would have been larger than the Arctic Ocean

Mars once had enough water to cover its entire surface, a study published today in Science suggests. Around 4.5 billion years ago, Mars was host to a body of water that was larger than the Arctic Ocean. At around .085 miles deep, the water would have covered Mars' surface, but it's more likely the pool was slightly greater than one mile deep. In that case, it would have covered around 20 percent of the planet, The Washington Post reports.

Mars also probably had seasons

The new findings come from a team of researchers who collected data via three large telescopes on Earth: the European Southern Observatory’s Very Large Telescope in Chile, and the Keck II telescope and NASA Infrared Telescope Facility in Hawaii. The scientists measured the amount of water and the amount of HDO — water's heavier form — in Mars' atmosphere. The test was similar to measuring the separation of oil and water, one of the study's authors, Geronimo Villanueva, told The Washington Post. "If you're losing material — which the atmosphere of Mars has been doing since it was formed — you'll lose more of the light material first," he said.

By measuring the ratio of H2O to HDO against their atmospheric rates of escape over nearly six years, the researchers were able to determine the planet's water content billions of years in the past. The research also indicates that Mars once contained several regional atmospheres and a climate divided into seasons.

mars-water

It's not news that water once existed on Mars. In 2013, grooves and slopes in the planet's surface hinted at recent water flow and last year, findings by NASA's Mars Curiosity rover suggested the planet's 96-mile-wide Gale Crater was once the location of a massive lake. But today's findings suggest that Mars' water supply was not fleeting. That Mars once hosted such a large body of water implies the planet may have been habitable for much longer than previously thought.

NASA plans to evaluate these findings from space with the launch of an orbiter in 2016.

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