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 – and finds that the planet may have been wetter and for longer than scientists may have thought.