NASA Banner
Spanish Synopsis
NMP Link
Search ST5
Skip Navigation


About ST5
ST5 Technology
ST5 Science
ST5 Education
Project Benefits
ST5 Partners
Quick Facts
New Millennium Program
Diagram of Earth's Magnetic Field

Earth's Magnetic Field

This diagram illustrates the solar wind flowing around and beyond Earth's magnetic shield. This shield, the magnetosphere, is bullet-shaped, with a nose that lies about 64,000 kilometers (just over 39,768 miles) toward the Sun. Its outer layer, the magnetosheath, is a transition layer where interplanetary space meets Earth's "suit of armor." The magnetosheath is just outside the boundary of the magnetopause that lies toward the Sun at approximately 10 Earth radii (65,000 kilometers or 40,000 miles). The magnetopause marks the point where the Earth's geomagnetic field "pauses," or ceases for the most part, to extend further outward. Here the Earth's magnetic field is so weak that the pressure of particles that escape Earth's gravity just equal the pressure within the solar wind.

As the solar wind bow shocks around our planet, it pushes Earth's magnetic field, which scientists call the "geomagnetic field," and "squashes" the field lines that face the Sun. At the same time, the solar wind plasma also exerts a drag, called a "tangential drag," that causes some of these field lines to be stretched into what appears to be a long tail, called the magnetotail. This "tail," which looks very much like a comet's tail, may extend to over more than 6,400,000 kilometers (just over 3,976,776 miles). It is divided into two lobes by a sheet of plasma, which ranges in temperature from 6000 kelvin to 35,100 kelvin (10,340 to 62,720 degrees Farenheit). Very hot compared to the temperatures we are used to on Earth!

Within the magnetosphere the hot solar wind plasma, which originated in the solar corona, mixes with the ionospheric plasma that moves up Earth's geomagnetic fields lines. This plasma is cool, in contrast to that of the solar wind. The movement of cool ionospheric plasma upward along these magnetic lines of force is usually termed the "polar wind" (just as the term "solar wind" describes the magnetic forces from the Sun).

Over the polar regions of both the Sun and the Earth, the magnetic lines of force extend almost radially (from the center) outward into the solar wind and the magnetosphere, respectively. Because the Lorentz Force does not stop charged particles from traveling along magnetic lines of force, they form magnetic natural channels for the outward flow of plasma from these bodies.

While the magnetosphere deflects most of the Sun's plasma, some charged particles do leak through the magnetopause and become trapped. They also enter the magnetosphere through the funnel-like openings called "cusps" over the north and south magnetic poles. Then geomagnetic storms and substorms occur. Such solar storms would have a devasting impact on our planet if we were not shielded by this magnetic field.


Bottom Spacer
Glossary News Archive Contacts/Credits Site Map Copyright
First Gov
Grey Spacer
Grey Spacer
Grey Spacer
Freedom of Information
President's Agenda
Performance Report
Privacy Act
Freedom to Manage
Grey Spacer
Grey Spacer
Grey Spacer
   Webmaster: Diane K. Fisher
   JPL Official: Nancy J. Leon

   Last Updated:  01 / 04