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Radioactive elements may be crucial to habitability of rocky planets

Christian Fernsby |
The amount of long lived radioactive elements incorporated into a rocky planet as it forms may be a crucial factor in determining its future habitability, according to a new study by an interdisciplinary team of scientists at UC Santa Cruz.

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That's because internal heating from the radioactive decay of the heavy elements thorium and uranium drives plate tectonics and may be necessary for the planet to generate a magnetic field.

Earth's magnetic field protects the planet from solar winds and cosmic rays.

Convection in Earth's molten metallic core creates an internal dynamo (the "geodynamo") that generates the planet's magnetic field.

Earth's supply of radioactive elements provides more than enough internal heating to generate a persistent geodynamo, according to Francis Nimmo, professor of Earth and planetary sciences at UC Santa Cruz and first author of a paper on the new findings, published November 10 in Astrophysical Journal Letters.

What they found is that if the radiogenic heating is more than the Earth's, the planet can't permanently sustain a dynamo, as Earth has done.

That happens because most of the thorium and uranium end up in the mantle, and too much heat in the mantle acts as an insulator, preventing the molten core from losing heat fast enough to generate the convective motions that produce the magnetic field.

With more radiogenic internal heating, the planet also has much more volcanic activity, which could produce frequent mass extinction events.

On the other hand, too little radioactive heat results in no volcanism and a geologically "dead" planet.


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