The Red Planet

The ocean on Mars was as deep as the Mediterranean and vast enough to cover the planet's entire surface, NASA scientists claimed in the study published Thursday in the journal Science. NASA researchers said that up to 20 percent of Mars had once been covered by water, which in some regions was greater than a mile (1.6 kilometers) deep.

"Our study provides a solid estimate of how much water Mars once had," said Argentine scientist Geronimo Villanueva, chief author of the study, who added that 87 percent of that water had been lost to space.

"With this work, we can better understand the history of water on Mars," said Villanueva, who chairs a host of research boards and works at NASA's Goddard Space Flight Center in Maryland.

Two types of water

Michael Mumma, a senior researcher at Goddard who co-authored the study, added: "With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting the planet might have been habitable for longer."

Using three of the world's most powerful telescopes, the scientists observed two slightly different forms of water found in the atmosphere. One is the familiar H2O, made with two hydrogen atoms and one oxygen.

The other is HDO, a naturally occurring variation in which one hydrogen is replaced by a heavier form, called deuterium.

By comparing the ratio of HDO to H2O, scientists were able to measure the enrichment and determine how much water had escaped into space.

The results of the study, NASA says, will lead to further research into the inhabitability of Mars, including its "environment, climate cycles, geology and biological potential." NASA is also continuing work on human spaceflight capabilities that would be required for future round-trip missions to the Red Planet, planned for the 2030s.