Planetary Science

... and Sulfur on Mars

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Science  13 Feb 2009:
Vol. 323, Issue 5916, pp. 854-855
DOI: 10.1126/science.323.5916.854d

Recent observations from satellites and the rovers shows that Mars has abundant sulfate minerals on its surface and that acidic alteration is widespread (carbonate minerals are rare). This is in marked contrast to the composition of even older rocks on Earth and the generally low sulfur content of Earth's crust. Gaillard and Scaillet show that these differences reflect the nature of each planet's internal and atmospheric evolution. Because of the lower overall pressure on Mars and its different core size and composition, the Martian mantle probably contains considerably more iron than Earth's. As a result, magmas derived from the mantle on Mars are several times richer in sulfur. Furthermore, low atmospheric pressure favors efficient degassing of this sulfur. The authors argue that thus as the atmosphere of Mars was lost to space, with pressure dropping from initial high values, its composition changed from water- and CO2-rich to sulfate-rich. This evolution can explain the observed history in which neutral hydrothermal alteration is superseded by widespread acidic alteration, and there is sufficient sulfur to cover the surface thickly in sulfate minerals. — BH

Earth Planet. Sci. Lett. 10.1016/j.epsl.2008.12.028 (2009).

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