The frozen ocean was captured by cameras aboard the European Space Agency's Express probe, which revealed an expanse of pack ice just north of the Martian equator, in Elysium, a region strewn with dormant volcanoes.
Dust kicked up by violent storms appears to have settled on the icy surface, outlining fragmented ice rafts covering an area as large as the North Sea. The water is believed to have seeped up from fissures several kilometres beneath the surface, perhaps carrying ancient microbes with it, before freezing some 5 million years ago.
Elsewhere, The New Scientist has reported that is losing little water to space, according to new research, and that much of its ancient abundance may still be hidden beneath the surface.
Dried up riverbeds and other evidence imply that once had enough water to fill a global ocean more than 600 metres deep, together with a thick atmosphere of carbon dioxide that kept the planet warm enough for the water to be liquid. But the planet is now very dry and has a thin atmosphere.The European Space Agency's Express spacecraft has revealed that the rate of water loss from solar winds is much lower that previously estimated. Its measurements suggest the whole planet loses only about 20 grams per second of oxygen and CO2 to space. Either some other process removed the water and CO2 or they are still present and hidden somewhere on Mars, probably underground in huge reserviors.