New evidence of oceans on Mars!

It’s been argued for years that Mars may have once had oceans of water, billions of years ago. Some catastrophe dried them up, making the evidence for them difficult to detect. Topographic (relief) maps look like there may have been two oceans in one spot, for example, separated by some time. There appear to be two separate shorelines, with one smaller, later ocean existing where there once had been a much larger ocean.

But that’s circumstantial. More direct evidence is needed.

So some scientists speculated a bit. Rocks containing elements like potassium, thorium and iron would get made in the highlands (near volcanoes), then get transported down into the lowlands. If there were an ocean there, those elements would get leeched out of the rocks by the water. Then, when the water evaporated, those elements would be deposited in a thin layer on the surface.

On board the orbiting probe Mars Odyssey is the Mars Gamma-Ray Spectrometer, a device which can measure the abundance of elements on the Martian surface. When it was trained on the lowlands of Mars, it found evidence to support the existence of those oceans! The elements in question were most abundant below the shorelines, as expected, when compared to regions outside (above) the shorelines. The regions with higher concentrations of potassium are marked in red and yellow in the map above, right where the lowlands are.

http://blogs.discovermagazine.com/badastronomy/2008/11/17/new-evidence-of-oceans-on-mars/