A third of Mars once covered by ocean: study

A huge, potentially life-giving sea likely covered more than a third of Mars some 3.5 billion years ago, according to a study released Sunday.

Spread over an area the size of the Atlantic Ocean, it would have straddled the north pole and contained the equivalent of a tenth of the water on Earth.

For decades scientists have argued as to whether the Red Planet once harboured bodies of water big enough to help nourish a true hydrological cycle marked by evaporation and rainfall.

Recent evidence suggests as much, but doubts remained.

To dig deeper, Gaetano Di Achille and Brian Hynek of the University of Colorodo in Boulder sifted through huge stores of images collected by NASA's Mars Orbiter Laser Altimeter (MOLA) in the late 1990s and other more recent European and US satellite-based monitoring systems.

The data was not new, but the researchers were the first to link up all available information on Mars' terrain into a single computer-driven model.

The study, published in Nature Geoscience, found 52 river-delta deposits scattered across the planet.

More than half occurred at about the same elevation, and thus probably marked the boundary of the once-massive sea.

All of these would have been connected either directly to the ocean, or to its groundwater table along with several large, adjacent lakes.

The scientists calculated that the ancient sea covered 36 percent of the planet's surface and contained about 124 million cubic kilometres (30 million cubic miles) of water.