Free Astronomy Magazine May-June 2015

13 MAY-JUNE 2015 SPACE CHRONICLES to provide such a high level of enrich- ment. The A rtist’s impressions and video that show how Mars may have looked about four billion years ago. The young planet would have had enough water to cover its entire sur- face in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres. [ESO/M. Kornmesser/N. Risinger] covered 19% of the planet’s sur- face — by comparison, the Atlantic Ocean occupies 17% of the Earth’s surface. “With Mars losing that much water, the planet was very likely wet for a longer period of time than previously thought, sug- gesting the planet might have been habitable for longer,” said Mi- chael Mumma, a senior scientist at Goddard and the second author on the paper. It is possible that Mars once had even more water, some of which may have been deposited below the surface. Because the new maps reveal microclimates and changes in the atmospheric water content over time, they may also prove to be useful in the con- tinuing search for un- derground water. volume of Mars’s early ocean must have been at least 20 million cubic kilometres. Based on the surface of Mars today, a likely location for this water would be the Northern Plains, which have long been considered a good candi- date because of their low-lying ground. An ancient ocean there w o u l d have n