Geodynamo

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Geodynamo

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You may remember that our magnetic field forms a protective bubble around Earth called the magnetosphere. It keeps solar winds and cosmic rays from scouring away our atmosphere, and protects spacecraft, satellites, astronauts, and air travelers. But where does the magnetic field come from? The inner core of Earth is very, very hot—about 6,000°C, the same as the surface of the sun. At that temperature, you’d expect it to be liquid or even gas. But because the pressure at the core is so extraordinary, about 2 million times what it is on the surface, the inner core stays solid. In fact, it’s 85 percent solid iron. The outer core of Earth is also mostly iron, but because the pressure is lower, it’s liquid. As lighter elements, at different temperatures, gradually rise through the liquid iron, they cause convection currents to form, like cream swirling in your coffee. Meanwhile, Earth’s rotation causes spinning eddies to develop. This somewhat-organized circulation of liquid metal creates electric currents, which charge Earth’s iron core, turning it into a giant electromagnet. The magnetic field in the core is thought to be more than 10 times stronger than on the surface —and strong enough to extend 400,000 miles into space. Which is what allows it to protect us from the hazards of space.

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