Planetary Science

Why No Clay Up North?

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Science  21 Oct 2011:
Vol. 334, Issue 6054, pp. 290
DOI: 10.1126/science.334.6054.290-b

The surface of Mars can be divided into two major regions: the northern lowlands and the southern highlands. The lowlands, covering around 1/3 of the planet, are thought to have once been the site of an ancient, great northern ocean. However, this hypothesis is at odds with the record of the presence of clay deposits. These sediments, whose formation requires the presence of liquid water, are widespread in the southern highlands but very scarcely distributed in the northern lowlands. Using a climate model, Fairén et al. determined the surface temperatures on early Mars, assuming a southern supercontinent and a northern ocean. The model temperatures imply that the northern ocean would have had to be a glacial ocean similar to the seas in Earth's polar regions. Calculations of the rate of clay formation at subzero temperatures support the lack of clays in the northern low-lands, because their formation would have been inhibited at those cold temperatures. Moreover, the presence of glaciers surrounding the northern ocean would have limited the transport of continental sediments into the ocean, as is the case in the Arctic and Antarctic coastal regions of Earth.

Nat. Geosci. 4, 667 (2011).

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