18.8 Magnetosphere
Yet another amazing zone of atmosphere is the magnetosphere. The magnetosphere extends thousands of kilometers above the earth's surface at distances equal to 10-25 earth radii or more (60.000-160,000 km). This region includes the exosphere of the earth's atmosphere.
James Van Allen discovered the magnetosphere in 1958 using information gathered by America's first artificial satellite, Explorer 1. More data revealed several rings or belts where most of the protons and electrons from the sun's solar wind end up trapped in the earth's magnetic field. These regions are fairly close to the earth compared to the outer boundaries of the magnetosphere (see Figure 18-16). In honor of Van Allen's discovery, these regions of dangerous radiation are called the Van Allen Belts. If you had continued your space elevator trip to the altitude of the Van Allen Belts, you would have received a lethal dose of solar radiation as you passed through. Manned spacecraft that travel through these belts of intense radiation must either be heavily shielded or move quickly past them.
Do you remember Earth's specially designed feature of the magnetic field discussed in Chapter 4? Strong solar storms would be especially deadly if the charged particles could strike the earth unhindered. But the magnetosphere shields the earth from the brunt of these storms. Read more about the features of the magnetosphere in the facet below. When the solar wind is especially strong, as it is during a solar flare (see Chapter 22). some of the charged particles trapped in the magnetosphere escape near the earth's magnetic poles into the lower regions of the atmosphere. There they collide with gas molecules in the atmosphere, producing beautiful aurora borealis (the "northern lights") and aurora australis (the "southern lights") near the respective poles.