PLANETARY SCIENCE: Martian Magnetism Getting Hotter

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Science  05 Mar 2004:
Vol. 303, Issue 5663, pp. 1439a
DOI: 10.1126/science.303.5663.1439a

While the world is focused on the rovers Spirit and Opportunity trundling across the surface, others are considering the structure and composition of the deep interior of Mars to determine if it ever had a magnetic field.

To generate a dynamo, Elkins-Tanton et al. assume a magma ocean on early Mars, a nearly completely molten planet caused by accretional heating. As the magma ocean crystallized, less dense layers would form beneath more dense layers, leading to an unstable stratification. Overturn of the unstable layers would bring colder materials down, causing conductive heating and initiating a brief but strong magnetic field.

In contrast, Williams and Nimmo suggest that the early core was hotter than the mantle because of rapid core formation. The temperature difference would produce enough entropy to drive a brief and early dynamo and a magnetic field that would magnetize the crustal rocks. In addition, the hot core should remain molten.

The molten mantle and molten core models are generally consistent with data from Martian meteorites. In time, data from the rovers may help to resolve these simmering debates. — LR

Meteorit. Planet. Sci. 38, 1753 (2004); Geology 32, 97 (2004).

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