Our planet is constantly swept by a "breeze" of charged particles from the Sun -- the solar wind. As they reach us, these particles are funneled toward the surface by Earth's magnetic field. They interact with the upper atmosphere, forming the glowing northern and southern lights.
But it turns out that Earth's magnetic field doesn't always let the particles in. Instead, they get through in clumps -- about once every eight minutes.
The solar wind is guided by the Sun's own magnetic field, which interacts with Earth's magnetic field on the planet's dayside. Several orbiting spacecraft have discovered that for awhile, the two fields form a sort of barrier, blocking most of the solar wind.
But about every eight minutes, the barrier falls apart as the two fields form a tight magnetic connection. The solar wind rushes through the portal, arriving at Earth in a gust. In addition to creating the beautiful aurorae, the solar wind also heats Earth's outer atmosphere, causing it to expand. And if it's dense enough, it can interfere with radio transmissions and cause other problems.
The scientists who study the Sun aren't sure just why the magnetic fields interact this way. In fact, much of the Sun's magnetic workings is still poorly understood. But a whole fleet of spacecraft is watching the Sun -- and its interaction with Earth -- to lay some of the mysteries to rest.
Tomorrow: rushing through the galaxy.
Script by Damond Benningfield, Copyright 2009
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