magnetosphere

The Greek term magnētis lithos ('Magnesian stone') named magnetic minerals found in Magnesia, an ancient region of Thessaly. The word 'magnesia' came to mean any magnetic material. Sphaira is Greek for 'sphere.' In 1959, astrophysicist Thomas Gold combined these at the University of Cambridge to describe what he theorized must be: a sphere of magnetic field surrounding Earth.

Nobody had directly observed this magnetic bubble. But Gold and others realized that Earth's magnetic field must extend far into space, creating a boundary where the solar wind could no longer push inward. The magnetosphere is shaped like a teardrop, compressed on the side facing the sun (about 65,000 km away) and stretched into a tail pointing away from the sun for millions of kilometers.

In 1963, the Explorer 12 satellite crossed the magnetosphere boundary for the first time, confirming Gold's theory. The magnetosphere was real. It protected Earth's upper atmosphere from the constant barrage of charged particles from the sun. Without it, the solar wind would strip away our atmosphere and render the planet uninhabitable.

Today, the magnetosphere is mapped by dozens of satellites. The Van Allen radiation belts are the magnetosphere's hottest regions. Auroras happen when solar particles breach the magnetosphere at the poles. The word we use for Earth's magnetic bubble is less than a century old. We live inside a force we couldn't name until we learned to leave the planet.