Mars once had an ocean that covered nearly one-fifth of its surface to a depth of maybe a mile, according to new research using Mauna Kea telescopes.

The findings, to be published Friday in the journal Science, add to the body of evidence that the Red Planet could have harbored life in its ancient past.

Scientists using the Keck Observatory and NASA Infrared Telescope Facility report that the water could have formed an ocean covering almost half of Mars’s northern hemisphere.

All this was some 3.7 billion years ago, toward the end of the planet’s wet Noachian period.

Nearly all of the water — 87 percent — has been lost to space, but some remains frozen at the planet’s poles. There could also be water reservoirs underground, scientists speculate.

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

Based on the surface of Mars today, a likely location for the water would be in the low-lying northern plains. An ancient ocean there would have covered 19 percent of the planet’s surface, the scientists said.

“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 senior scientist at Goddard, also an author of the paper.

The research team used the Near-Infrared Spectrograph on the Keck Observatory to study signatures of water in the planet’s atmosphere.