NASA's Space Place
Earth’s Magnetic Shield
By Linda Hermans-Killam
National Aeronautics and Space Administration
Thousands of miles beneath our feet, flowing electrons create a powerful force that protects life on Earth. This effect is called a magnetic field. But what creates this magnetic field?
Deep, deep below the ground lies center of the Earth, also called its core. It is a place of incredibly high temperatures and pressures.
Earth's core is made up mostly of metals, like iron and nickel. When metals are very hot, their atoms move so fast that they can no longer stay solid and they melt into liquid. Although the inner part of the core is very hot, the metals there cannot melt. This is because the pressure there is too high from the weight of the rest of the Earth above it. The high pressure makes it difficult for these metal atoms to move around.
But in the outer part of the core, the pressure is lower and the metals there can melt. The molten metal in the outer core flows in high speed currents as the Earth spins. Within this molten metal are electric charges. These flowing electric charges create a strong magnetic field. In fact, Earth's magnetic field is so powerful that it reaches out into space and surrounds the entire Earth!
Earth's magnetic field is very important because it protects us from harmful radiation from space. It also shields us from the solar wind—a stream of high speed particles that flows from the sun. These particles travel at speeds of about one million miles per hour! Thankfully, most of these particles bounce off Earth's magnetic field and pass around the Earth. If Earth had no magnetic field, these particles would erode away our atmosphere. This actually happened on our neighbor planet, Mars. When the magnetic field surrounding Mars was weakened, most of its atmosphere was stripped away by the solar wind.
Sometimes particles from the solar wind get trapped in Earth's magnetic field. When too many particles get trapped, some overflow into our atmosphere near Earth's magnetic poles. Here they collide with atoms and molecules in the atmosphere, creating beautiful displays of lights called auroras. Although our magnetic field can't block every particle from space, the ones that slip through make for an awesome show!
To learn more about auroras, visit the NASA Space Place: http://spaceplace.nasa.gov/aurora/en/
An illustration of Earth's magnetic field. Image credit: NASA
Artist's depiction of energetic charged particles trapped by Earth's magnetic field.
Image credit: NASA/Goddard Space Flight Center/Scientific Visualization Studio