Evidence suggests a cold ocean existed on early Mars
A cold glacier-rimmed ocean may have covered the northern lowlands of Mars early in its history, research suggests.
The coastline may have resembled that of Greenland or Norway.
Scientists believe the ocean's existence helps explain a lack of minerals called phyllosilicates in the region. It also explains features likely to have been caused by large glaciers around the ocean basin.
These include accumulations of glacier-transported debris called moraines and "fretted" terrain.
Computer simulations indicated a big temperature difference between warmer equatorial regions of Mars and the much colder poles four billion years ago. As a result, any ocean in the northern lowlands would have been near-freezing.
A wall of glaciers skirting the ocean would have prevented the deposition of phyllosilicates originating in the equatorial highlands.
The minerals are associated with liquid water. Previously their absence in the northern lowlands cast doubt on previous speculation that an ocean existed there.
Dr Alberto Fairen, from the American space agency NASA's Ames Research Centre at Moffett Field, California, and colleagues, wrote in the journal 'Nature Geoscience': "We conclude that inefficient heat transport from the equator to the poles on early Mars, due to the absence of Earth-like equator-to-pole oceans, resulted in a steep latitudinal gradient of temperatures in both hemispheres, with warmer mid and equatorial areas, and glacial polar regions.
"As a consequence, if a northern ocean existed on early Mars, it was very cold. Glaciers rimming a cold northern ocean would have prevented a significant fluvial transport of phyllosilicate-rich materials from the highlands into the lowlands."