Did you know Mars may once have had an ocean? 🌊 Scientists believe that billions of years ago, over 20% of Mars’s surface—the planet’s northern plains - may have been covered by a vast ocean. It wasn’t shallow either: estimates suggest it reached nearly a mile deep, reshaping the planet’s landscape. Ancient shorelines, massive valleys, and water-formed minerals point to a Mars that once looked dramatically different. Understanding this watery past helps scientists trace how the Red Planet chang