In a study released on Thursday, NASA scientists revealed that Mars once had enough water to form a large but shallow ocean covering half of its northern hemisphere. This new discovery could change the playing field as the search continues for evidence of organic life on our neighboring planet.

Researchers for the project monitored the atmosphere of Mars for six years to gather data about the amount and type of water that can presently be found on the Red Planet. After years of careful observation, scientists say that a giant ocean stretched across the surface of the planet 4 billion years ago, but that as much as 87 percent of the water on Mars has since been lost to space because of Mars’ weak atmosphere. The ocean would have been only about a mile deep.

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

This new estimate about the volume of water on Mars could have an impact on how scientists search for signs of life on the Red Planet. “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,” said Michael Mumma, a co-author of the study.

The NASA rover Curiosity is currently combing the surface of Mars for evidence of organic life, taking soil samples and analyzing the atmosphere for possible tell-tale signatures like methane. The new information about the water history of Mars was gathered using telescopes at the Keck Observatory, NASA’s Infrared Telescope Facility, and ESO’s Very Large Telescope in Chile.