NASA scientists have discovered Mars may once have had a massive ocean covering half of its northern hemisphere. The research looked at the planet 4.5 billion years in the past and calculated that the water could have been 450 feet (137 meters) deep, according to Ars Technica. However, since the planet is not completely flat, scientists believe that the water likely pooled in the lower depressions of the planet's northern hemisphere, covering about a fifth of the Martian surface. Continue reading…