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Iron Snow behind Mercury's Magnetism

The core of Mercury may have flakes of iron falling like snow and initiating a global magnetic field. Cynthia Graber reports.

[The following is an exact transcript of this podcast.]

On Earth, snow crystals, as we all know, form from frozen water. But scientists believe there are also flakes that fall on Mercury—and they’re made of iron. They published their findings in the journal Geophysical Research Letters. Investigators have been trying to figure out why Mercury is the only other terrestrial planet in our solar system that has a global magnetic field. It's about one hundred times weaker than earth's. No previous models have been able to predict what would cause this type of situation. So researchers at the University of Illinois and Case Western University set up an experiment to try to figure it out.

They created a molten iron and sulfur mixture—similar to Mercury's core. They subjected the mix to high temperatures and pressures. Then they analyzed what happened in this Mercury model. Turns out that as the outer core cools, the iron forms what researchers call cubic “flakes” that slowly fall to the core's center. As the iron snow falls, the sulfur-rich liquid rises. Researchers believe these currents produce the weak magnetic fields—and Mercury's iron snow.

—Cynthia Graber   

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