This is a composite image illustrating what Mars would look like today if it still had the massive amount of water researchers believe was present at its formation. If the primordial Martian ocean still existed, it would cover large areas of the planet, represented by the blue regions.
Although Mars is now very dry, scientists observing the Martian atmosphere with NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) spacecraft, combined with other research, estimate that Mars could have been born with more water in proportion to its mass than the Earth. If the initial quantity of water on Mars could have been evenly distributed across the planet somehow, it would have been equivalent to a global Martian ocean at least three-quarters of a mile (1.25 kilometers) deep. This is 1.3 times more water per mass than the Earth.