One hundred and fifty million kilometres away, the Sun exhales. A million tonnes of charged plasma per second.
Racing outward at four hundred kilometres per second. It has been doing this for four and a half billion years.
Earth stands in the way.
A magnetic shield — invisible, enormous — deflects the wind around the planet.
This rhythm is four and a half billion years old—older than life on Earth. The magnetosphere has never stopped breathing.
The Moon passes through the magnetotail once every orbit. Sixty Earth-radii out.
150 million km

# The Magnetosphere

Earth's invisible ocean

Deep inside Earth, a core of liquid iron has been convecting for four and a half billion years. That churning metal generates the magnetic field that inflates this entire structure—and drives a circuit that reaches from the core to the edge of space.

## The Circuit

Kristian Birkeland proposed this circuit in 1908. It took sixty years for satellites to prove him right. The current descends along field lines, crosses the polar ionosphere, rises on the other side, and returns to space. Where it enters the atmosphere, atoms glow: the aurora.

The magnetopause normally holds. Solar wind deflects around it—nothing gets through. But the Sun is not constant. It sends thick plumes of magnetized plasma—coronal mass ejections—that can overwhelm the magnetosphere. When the Sun's magnetic field turns against Earth's, the shield's weak point breaks open. What follows is a geomagnetic storm.

## The Gate

When the gate opens, a billion watts of power pour into the magnetosphere—driving currents along field lines, heating plasma, stripping satellites of their electronics, and lighting the aurora across the sky. In the largest storms, the magnetopause is pushed inside geosynchronous orbit—the protective envelope compresses until the satellites that depend on it are left exposed in the raw solar wind.

This is happening right now, above your head, whether anyone is watching or not.