The Sun is leaking
What Is the Solar Wind?
A constant stream of particles blows out of the Sun and past every planet.
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Step 1 of 5
The Sun's outer layer is unbelievably hot.
Its surface is about 5,500°C, but the thin corona above it reaches over a million degrees. Nobody fully agrees why it is hotter than the surface.
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At that heat, particles outrun gravity.
Heat means particles moving fast. In the corona they move so fast that even the Sun's enormous gravity cannot hold them, and they stream away.
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The stream fills the whole solar system.
It blows outward in every direction at 400 to 800 km per second, past every planet, out beyond Pluto, to a boundary called the heliopause.
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Step 4 of 5
Earth's magnetic field deflects it.
Our planet's magnetism forms a shield that splits the stream and steers most of it around us. Without that shield, the wind would slowly strip our air away.
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Step 5 of 5
You can see where it gets through.
Near the poles the field lets particles in, and they crash into the air and make it glow. That is the aurora — the solar wind made visible.
Big solar storms can knock out satellites and power grids. In 1989 one blacked out the whole of Quebec.
The short version
The solar wind is the Sun constantly leaking particles — and Earth's magnetism is what keeps them off us.
Try it yourself
Hold a hairdryer and put your hand behind a book. The book splits the stream — that is Earth's magnetic field.
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