A hypothetical picture of Mars 3.6 billion years ago, when an ocean may have covered nearly half the planet. The blue areas show the depth of the ocean filled to the shoreline level of the ancient ...

Previous studies estimated that there could be enough water deep underground on Mars to cover the surface in a global ocean between 0.62 to 1.24 miles (1 and 2 kilometers) deep.

The Mars ocean theory hatched in the 1970s after spacecraft imagery showed an apparent large shoreline and seabed-like indentation. Some scientists discounted the idea since the shore seemed irregular ...

The “Mars ocean theory” has long been the topic of discussion among scientists and cartographers due to Mars’s geography, which suggests a large northern ocean once existed on its surface.

The total volume of hidden water could flood the whole of Mars' surface with an ocean 1,700 to 2,560 feet [520 to 780 metres] deep, around the same volume of liquid that is contained within ...

A new study revealed that humans have "directly observed" less than 0.001% of the deep seafloor, despite the oceans covering over 70% of Earth's surface.