Dry, dusty Mars once had an ocean that held as much water as the Arctic Ocean and covered a larger share of the Red Planet’s surface than the Atlantic Ocean does on Earth, according to a surprising new study.

The findings, described online in the journal Science, examined the patterns in the Martian atmosphere to try to understand how much water it has lost in the last few billion years.

As the scientists examined their surprising findings, “the story started to make sense,” said lead author Geronimo Villanueva, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Researchers have gone back and forth on whether Mars held enough water for long enough to have given microbial life a sporting chance to emerge on the Red Planet. NASA’s Curiosity rover has tested the air and found the Martian atmosphere may have been stripped so long ago there was a slim chance for life; but studies of rocks that the rover has drilled in Gale Crater have revealed signs of a series of lakes that lasted for many millions of years.