We’ve known water was on Mars in the past, but how much exactly was there? Fresh NASA research suggests Mars had more water than Earth’s Arctic ocean.

“Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new paper. “With this work, we can better understand the history of water on Mars.”

To figure it exactly how much water ancient Mars had, researchers used three of the world’s most powerful infrared telescopes: The W.M. Keck Observatory, the Very Large Telescope (VLT) and the NASA Infrared Telescope Facility.

W.M. Keck Observatory

W.M. Keck Observatory

These observations revealed the atmospheric ratios of normal (H2O) to heavy water (HDO) molecules. The HDO is still on Mars today, in its polar ice caps. Normal water (H2O) would have been lost to space many years ago.

“Now, we know that Mars water is much more enriched than terrestrial ocean water in the heavy form of water, the deuterated form,” said Michael Mumma, NASA Goddard senior scientist, in the video below.

The HDO : H2O ratio on Mars is 1 : 400, compared to Earth’s 1 : 3,200.

Armed with this ratio, researchers can estimate the amount of water ancient Mars lost. Just 13% of Mars’ ancient ocean is on the surface today, in the polar ice caps. 87% was lost to space.

A Martian Ocean

Would all of this water have been in the form of an ocean? Mumma says it would. In an area called the Northern Plains, an ocean covering 20% of Mars would have existed. This ocean would have been nearly one mile deep according to Villanueva.

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“It’s deep – not as deep as the deepest points of our oceans, but comparable to the average depth of the Mediterranean Sea,” said Villanueva.

The new research means Mars would have been wetter for much longer than previously thought. NASA’s Curiosity rover already showed Mars was wet for 1.5 billion years. Now, researchers find it was wet for even longer.

“Ultimately we can conclude this idea of an ocean covering twenty percent of the planet, which opens the idea of habitability, and the evolution of life on the planet,” said Villanueva.

Top image: Chasma Boreale (polar ice sheet)

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