Mars Once Had A Vast Ocean Covering One-Fifth Of Its Surface, New Research Suggests

Scientists have long known there was once water on Mars, but just how much?

New research suggests that the Red Planet was way wetter than scientists thought. In fact, it seems that large portions of the Martian surface were flooded under a vast ocean--and that seems to have increased the odds that Mars was once habitable.

The research, an analysis of chemical "signatures" in the Martian atmosphere, indicates that some 4.2 billion years ago a body of water bigger than the Arctic Ocean covered nearly one-fifth of the planet's surface. This ocean likely contained a whopping 5 million cubic miles of water, with a maximum depth of one mile.

“Ten years ago, the story of water on Mars was an occasional flood of rocky debris every 100m years that then switched off again," John Bridges, a Leicester University planetary scientist who works on NASA’s Curiosity rover mission, told The Guardian. "We now know it’s more continuous. There were long-standing bodies of water: lakes, deltas and perhaps even seas. It seems to me that we have excellent evidence that Mars was once habitable, though whether it was ever inhabited is not clear."

For the research, scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland analyzed observations of the atmosphere above Mars' north and south poles made over the course of six years by the European Southern Observatory’s Very Large Telescope in northern Chile and the W.M. Keck Observatory and NASA Infrared Telescope Facility in Hawaii.

The scientists compared the atmospheric concentrations of "normal" water (H2O) to "heavy water" (HDO), in which one hydrogen atom is replaced with an atom of the isotope deuterium. They discovered that the concentration of deuterium over the polar ice caps is now much higher than is seen in Earth's oceans.

The finding suggests ancient Mars must have lost an ocean's-worth of normal water, as the normal water would have evaporated into space while the heavy water would have been trapped in the planet's water cycle. The scientists estimate that the total volume of water on the planet was once roughly 6.5 times greater than the amount of water found in the polar ice caps today.

“With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting it might have been habitable for longer,” Michael Mumma, a senior scientist at Goddard and a co-author of a paper describing the research, said in a written statement.

The paper was published online March 5 in the journal Science.